WO2018140972A1

WO2018140972A1 - Multilayer devices and methods of manufacturing

Info

Publication number: WO2018140972A1
Application number: PCT/US2018/016029
Authority: WO
Inventors: Joseph Capobianco; Christian Martorano; Daniel Declement
Original assignee: TBT Group, Inc.
Priority date: 2017-01-30
Filing date: 2018-01-30
Publication date: 2018-08-02

Abstract

This disclosure relates to micro-scale and nano-scale multilayer devices ("MLD") and methods of manufacturing same. In one illustrative embodiment, a method of a manufacturing an MLD may comprise tape casting a slurry comprising a ceramic powder and a binder to form a plurality of green sheets, forming one or more of the plurality of green sheets into a desired shape, depositing a circuitry pattern onto one or more of the plurality of green sheets, laminating the plurality of green sheets with each green sheet at least partially overlapping at least one adjacent green sheet, and cofiring the laminated plurality of green sheets to form the multilayer device.

Description

MULTILAYER DEVICES AND METHODS OF MANUFACTURING

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Patent Application Serial No.

62/452,335, filed on January 30, 2017, the entire disclosure of which is incorporated herein by reference.

TECHNICAL FIELD

[0002] The present disclosure relates, generally, to micro-scale and nano-scale multilayer devices ("MLD") and methods of manufacturing the same.

SUMMARY OF INVENTION

[0003] Illustrative embodiments of the invention are described in the following enumerated clauses. Any combination of the following clauses is contemplated, along with any applicable combination with the embodiments described in the Detailed Description of Illustrative Embodiments below.

[0004] 1. A method of manufacturing a multilayer device, the method comprising: tape casting a slurry comprising a ceramic powder and a binder to form a plurality of green sheets; forming one or more of the plurality of green sheets into a desired shape; depositing a circuitry pattern onto one or more of the plurality of green sheets; laminating the plurality of green sheets with each green sheet at least partially overlapping at least one adjacent green sheet; and cofiring the laminated plurality of green sheets to form the multilayer device.

[0005] 2. The method of clause 1, wherein the tape casting comprises: spreading the slurry to form a paste on a substrate; and blading the paste to form a thin layer of slurry.

[0006] 3. The method of clause 2, wherein the blading comprises drawing the paste under a blade to form the thin layer of slurry. [0007] 4. The method of any preceding clause, further comprising marking one or more of the plurality of green sheets for alignment.

[0008] 5. The method of clause 4, wherein marking the one or more of the plurality of green sheets comprises forming location holes for alignment.

[0009] 6. The method of clause 5, wherein forming the location holes comprises at least one of punching, dissolving, etching, abrading, and cutting the one or more of the plurality of green sheets.

[0010] 7. The method of any preceding clause, wherein depositing a circuitry pattern comprises printing at least one of electrodes, wiring, and via fillings onto the one or more of the plurality of green sheets.

[0011] 8. The method of clause 7, wherein the printing is screen printing.

[0012] 9. The method of any preceding clause, wherein the laminating comprises aligning at least two of the plurality of green sheets.

[0013] 10. The method of clause 9, wherein the aligning comprises stacking the at least two of the plurality of green sheets such that portions of the circuitry pattern on each of the at least two of the plurality of green sheets are connected with each other.

[0014] 11. The method of clause 9 or clause 10, wherein the aligning is performed using charge coupled device (CCD) cameras and an x-y angle stage.

[0015] 12. The method of any preceding clause, wherein the laminating comprises applying pressure and heat to the plurality of green sheets to bond adjacent green sheets.

[0016] 13. The method of any preceding clause, wherein the laminating comprises cold isostatic pressing to increase green density.

[0017] 14. The method of any preceding clause, wherein the cofiring comprises burning out the binder at a temperature no greater than 500 °C.

[0018] 15. The method of clause 14, wherein the cofiring comprises final sintering at a temperature of at least 1000 °C. [0019] 16. The method of any preceding clause, wherein the cofiring comprises sintering by at least one of heat, pressure, electromagnetic radiation, and electric current.

[0020] 17. The method of any preceding clause, wherein the cofiring comprises sintering by at least one of liquid phase sintering and reactive sintering.

[0021] 18, The method any preceding clause, further comprising depositing metallization layers to complete electrical connections.

[0022] 19. The method of any preceding clause, further comprising poling the plurality of green sheets to orient ferromagnetic domains.

[0023] 20. The method of clause 19, wherein the polling comprises applying an electric field to the plurality of green sheets.

[0024] 21. The method of any preceding clause, wherein the ceramic powder is an ultrafine powder.

[0025] 22. The method of any preceding clause, wherein the ceramic power is synthesized by a wet-chemistry-based processing route.

[0026] 23. The method of clause 22, wherein the wet-chemistry-based processing route is one of chemical co-precipitation, sol-gel process, and hydrothermal reaction.

[0027] 24. The method of any preceding clause, wherein the binder is a polymeric binder.

[0028] 25. The method of any preceding clause, wherein slurry includes a solvent for dissolving the binder.

[0029] 26. The method of any preceding clause, further comprising machining one or more of the plurality of green sheets to a desired dimension prior to the cofiring.

[0030] 27. A multilayer cantilever preform comprising: a preform stack including a plurality of sheets stacked together such that adjacent sheets at least partially overlap, each of the plurality of sheets comprising ceramic; and a circuitry pattern arranged on one or more of the plurality of sheets; wherein at least one cantilever arm is defined by at least a portion of the preform stack, the at least one cantilever arm including at least one piezoelectric layer and at least one non-piezoelectric layer.

[0031] 28. The preform of clause 27, wherein one or more of the plurality of sheets includes a via hole defined though a thickness of the sheet.

[0032] 29. The preform of clause 28, wherein a portion of the circuitry pattern extends through the via hole.

[0033] 30. The preform of clause 29, wherein the portion of the circuitry pattern that extends through the via hole fills the via hole.

[0034] 31. The preform of any one of clauses 27-30, wherein the ceramic of the plurality of sheets has a theoretical density of at least 95% after burn out of a binder.

[0035] 32. A multilayer cantilever green preform comprising: a preform stack including a plurality of green sheets stacked together such that adjacent green sheets at least partially overlap, each of plurality of green sheets comprising ceramic and a binder dissolved in a solvent; and a circuitry pattern arranged on one or more of the plurality of green sheets; wherein at least one cantilever arm is defined by at least a portion of the preform stack, the at least one cantilever arm including at least one piezoelectric layer and at least one non- piezoelectric layer.

[0036] 33. The preform of clause 32, wherein the binder has a glass transition temperature of 20 °C or less.

[0037] 34. The preform of clause 32 or clause 33, wherein the solvent is free of volatile organic compounds (VOCs).

[0038] 35. The preform of any one of clauses 32-34, wherein the solvent is free of hazardous air pollutants (HAPs).

[0039] 36. The preform of any one of clauses 32-35, wherein one or more of the plurality of green sheets includes a via hole defined though a thickness of the sheet. [0040] 37. The preform of clause 36, wherein a portion of the circuitry pattern extends through the via hole.

[0041] 38. The preform of clause 37, wherein the portion of the circuitry pattern that extends through the via hole fills the via hole.

BRIEF DESCRIPTION OF DRAWINGS

[0042] The concepts described in the present disclosure are illustrated by way of example and not by way of limitation in the accompanying figures. For simplicity and clarity of illustration, elements illustrated in the figures are not necessarily drawn to scale. For example, the dimensions of some elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference labels have been repeated among the figures to indicate corresponding or analogous elements. The Detailed Description of Illustrative Embodiments below particularly refers to the accompanying figures in which:

[0043] FIG. 1 is a simplified diagram illustrating one embodiment of a piezoelectric microcantilever sensor ("PEMS");

[0044] FIG. 2 is a series of simplified diagrams illustrating deformation of the PEMS of

FIG. 1 under the influence of an electric field;

[0045] FIG. 3 is a simplified flow diagram illustrating one embodiment of a method of manufacturing MLD;

[0046] FIG. 4 is a simplified diagram illustrating one embodiment of a tape casting process;

[0047] FIG. 5 is a series of simplified diagrams illustrating several embodiments of

MLD incorporating one or more cantilevers;

[0048] FIG. 6 is a series of simplified diagrams illustrating one embodiment of electroconductive patterning for an MLD incorporating a single cantilever; [0049] FIG. 7 is a series of simplified diagrams illustrating one embodiment of electroconductive patterning for an MLD incorporating a cantilever array; and

[0050] FIG. 8 is a series of simplified diagrams illustrating embodiments of MLD incorporating clamped cantilevers.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODFMENTS

[0051] While the concepts of the present disclosure are susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the figures and will be described herein in detail. It should be understood, however, that there is no intent to limit the concepts of the present disclosure to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives consistent with the present disclosure and the appended claims.

[0052] References in the specification to "one embodiment," "an embodiment," "an illustrative embodiment," etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may or may not necessarily include that particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to effect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

[0053] In the drawings, some structural or method features may be shown in specific arrangements and/or orderings. However, it should be appreciated that such specific arrangements and/or orderings may not be required. Rather, in some embodiments, such features may be arranged in a different manner and/or order than shown in the illustrative figures. Additionally, the inclusion of a structural or method feature in a particular figure is not meant to imply that such feature is required in all embodiments and, in some embodiments, may not be included or may be combined with other features.

[0054] Referring now to FIG. 1, one illustrative embodiment of a PEMS 100 is shown in a simplified diagram. The PEMS 100 shown in FIG. 1 has a length, L, and a width, w, and comprises a piezoelectric layer of thickness tp, density, rp, and Young's modulus Yp, and a non-piezoelectric layer of thickness tn, density, rn, and Young's modulus Yn. Because of the converse piezoelectric effect, when an electric field is applied to the polarization (thickness) direction of the piezoelectric layer, it will elongate or shrink along the length and width directions. However, the non-piezoelectric layer does not deform thereby constraining the movement of the piezoelectric layer and resulting in bending of the cantilever structure, as illustrated in FIG. 2. When an AC field is applied to the PEMS 100, it will bend up and down resulting in flexural (bending) vibration.

[0055] The ith-mode flexural resonance frequency, f, may be written as:

2

where ' is the dimensionless ith-mode eigen value, M_e is the effective mass, and k is the spring constant. The effective mass, M_e, may be written as:

M_e = 0.234Lw(p_pt_p + pj_n ) (_{Eq 2}

The spring constant, k, may be written as:

Y_efft³w

^4L (Eq. 3),

where Y_e/fis the effective Young's modulus of the PEMS 100, as given by:

Y + Y + 2Y_pY_nr_pr_n {2rl + 2r_n ² + 3r_pr_n )

with ^{tp + t}" (Eq. 5) and ^{tn + t}p (Eq. 6)

[0056] The resonance frequency of the PEMS 100 can be measured by electrical means.

For instance, an impedance analyzer may be used to measure phase angle (q) versus frequency spectrum, where q = tan^"1(Im(Z)/Re(Z)) is the phase angle of the complex electrical impedance, Z, and Im(Z) and Re(Z) are the imaginary and real parts of the electrical impedance. Off resonance, the cantilever behaves as a capacitor with a phase angle close to -90°. At or near resonance, the in-phase flexural motion gives rise to a peak in the real part, Re(Z), of the electrical impedance, and hence a peak in the phase angle. The shape of this phase angle vs frequency curve is a measure of device performance. Generally speaking, sharper curves allow for more accurate and repeatable device performance.

[0057] In biosensing, actuator, and energy harvesting applications (among other applications), it is desirable for micro-scale and nano-scale resonators to display a high quality factor ("Q factor"). The Q factor of a resonator is a measure of the strength of the damping of its oscillations. The Q factor via resonance bandwidth may be defined as the ratio of the resonance frequency v₀ and the full width at half-maximum ("FWFDVI") bandwidth δν of the resonance such that:

Q= vo/ δν (Eq. 7).

[0058] As the resonant frequency of a device is highly dependent on the geometry of the device, it will be appreciated by those of skill in the art that, in order to obtain devices with high Q factors, manufacturing methodologies should allow precise control over device geometry. Such control will allow for high accuracy and repeatability in device to device performance. Furthermore, it is desirable that methods of device fabrication be scalable and economical for large-scale industrial applications.

[0059] The present disclosure provides, among other things, repeatable manufacturing techniques and methodologies useful for producing MLD incorporating piezoelectric resonators with high Q factors. More specifically, according to the present disclosure, MLD may be manufactured using techniques and methodologies similar to those which are used to produce high temperature cofired ceramics (HTCC) and low temperature cofired ceramics (LTCC). Such MLD may be utilized in biosensors, energy harvesters, and actuators, among other applications.

[0060] Referring now to FIG. 3, one illustrative embodiment of a method 300 of manufacturing MLD is illustrated as a simplified flow diagram. As described in greater detail below, the method 300 generally involves tape casting individual sheets, which are subsequently, cut, electroded, laminated, and sintered. The method 300 is suitable for reproducible, high-volume production of MLD with thinner piezoelectric layers. It will be appreciated that, in some embodiments, the method 300 may involve additional and/or different steps to those illustrated in FIG. 3. For instance, in some embodiments, the method 300 may also involve cold isostatic pressing for the laminated tapes, resulting in higher green density in order to reproducibly control sintering shrinkage. As another example, following sintering, additional machining of the MLD can be used to further tailor the geometries of the MLD (e.g., if near net form shrinkage is obtained).

[0061] The first several steps of the method 300 relate to formation of a slurry for the tape casting process. The slurry components generally consist of ceramic powders, dispersants, polymeric binders, solvents, and plasticizers. The balance between the ratios of these components facilitates control of material performance and shrinkage, which ultimately dictate final device performance.

[0062] Slurry preparation begins with mixing ceramic powders in the presence of solvent and dispersing agent in order to reduce the powder agglomerates to the primary particles and coat each primary particle with a steric barrier, such as in a non-aqueous dispersion. Due to the surface chemistry (the interaction of the ceramic particles with the solvents), dispersing agents, such as polymeric dispersants and dispersing resins, can be incorporated to facilitate wetting, deagglomeration, and stability. In addition to dispersing agents, various milling and mixing techniques may be employed to break down the agglomerates (e.g., ball milling, bead milling, attrition milling, etc.).

[0063] Ceramic powders have been traditionally prepared by solid-state reaction processes using oxides as the starting materials. Conventional methods require a high calcination temperature, usually leading to inevitable particle coarsening and aggregation of the powders. The presence of hard particle agglomerates may result in poor microstructure and properties of the ceramics. One technique to avoid such hard particle agglomerates is to use ultra-fine, calcined powders to fabricate ceramic components. These ultrafine powders can be synthesized by wet-chemistry-based processing routes (e.g., chemical co-precipitation, sol-gel process, and hydrothermal reaction). However, for many of these wet-chemistry-based processes, the precursor powders must be calcined at a temperature 500-900°C to get the designed crystallographic phase. Also, wet-chemistry-based methods usually involve chemicals that are sensitive to moisture or light, making them difficult to utilize, and may be very time consuming. However, a particular advantage of wet-chemistry-based techniques is that the shrinkage variation between batches is more forgiving, meaning less geometrical anomalies arise.

[0064] Once the ceramic particles are deagglomerated and stabilized in the presence of solvent and dispersants, a polymeric binder is introduced to enhance dispersion stability, and provide strength to the final coating. The polymeric binder is dissolved in the solvent or suspended (in the form of an emulsion) and serves as "glue," which will tie the ceramic particles together in the dried film. The powder is encased in the polymeric resin during the slip preparation, but the resulting green tape is a continuous phase resin that surrounds entrapped particles. As it is the only continuous phase in the green tape, the binder has the greatest effect on properties such as strength, flexibility, plasticity, ability to laminate, durability, toughness printability, smoothness, and dimensional stability. [0065] During the drying process the solvent evaporates from the system, and the binder forms a film. In some embodiments, these film formers are polyvinyls, celluloses, or polyacrylates. Factors that influence polymer selection may include solubility, viscosity, cost, strength, glass transition temperature, ability to modify glass transition temperature, decomposition temperature and kinetics, sintering atmosphere, and ash residue. The use of long chain alcohol (e.g. 4 carbon atoms or higher in the chain) esters of acrylic or methacrylic acid yield virtually no ash upon decomposition, have fast burnout, and are often preferred for advanced electro-ceramic materials.

[0066] The polymer chain length of the binder may vary considerably. Generally, shorter chain polymers may be used to generate slips with higher ceramic loadings because they will display lower viscosities, and burnout faster at lower temperatures. A trade-off associated with lower molecular weight polymers is the shorter chains often generate weaker films, thus requiring a larger volumetric content. The larger volumetric content can make shrinkage control more difficult during burn-out and sintering, but can be repeatable through systematic process development.

[0067] During the drying process, the solvent will evaporate from the system, leaving void space behind. Some of the empty space will dissipate as the body contracts due to drying shrinkage, while the remaining space previously occupied by the solvent will generate porosity. Residual porosity contributes to further processing variables such as compressibility, strength, printability (ink adhesion), ability to laminate, and shrinkage. In addition to these concerns, the choice of solvent often depends on ability to wet the ceramic particles, compatibility with the selected binder, and ability to dry off in a controlled manner which does not lead to cracking, blistering, skinning, or excessive shrinking while drying. Furthermore, the use of solvents without hazardous air pollutants ("HAP") and volatile organic compounds ("VOC") are often preferred for volume manufacturing. [0068] The term plasticizer is loosely used to describe any additive that imparts either flexibility or plasticity to the green tape, and could essentially be considered a very slow evaporating solvent. A plasticizer may be used to increase the binder's flexibility, workability, and/or distensibility. The mechanism of action depends upon the type of plasticizer (type 1 or type 2). Plasticizers may provide the advantage of facilitating handling, punching, and shaping the green tape, but the disadvantage of diminished dimensional stability. The chemistry and quantity of plasticizer in the slurry formation may be optimized in such a manner that the tape can be processed in to the MLD without sacrificing control over the final device geometry. A preferred method to maintain flexibility, and greatly extend shelf life of such thin layers of green tape, is the use of binders with a low glass transition temperature (Tg). For example, blending in a binder with a T_g of 20°C or less will plasticize the primary binder, and provide smooth, uniform removal of organic material during binder burnout.

[0069] In summary, the slurry may be formulated in such a way that cast ceramic structures with the desired phase and physical characteristics are generated. The structure should typically be dense, and designed in such a way that the shrinkage is well controlled and reproducible on a lot-to-lot basis.

[0070] To obtain a controlled tape thickness, a doctor blade machine may be used. One illustrative example of such equipment is shown in FIG. 4. Casting is accomplished by spreading the slurry formulation to form a paste on a moving carrier substrate and removing some of the volatiles. The preferred viscosity profile for the mill base, or dispersion, is Newtonian, or near Newtonian, as this is an indicator of good dispersion of the ceramic powder. However, the final slurry used for doctor blading may be a non-Newtonian fluid containing a mixture of ceramic powder, solvent, and polymer resin, plasticizer, etc., which displays a shear- thinning, or pseudoplastic, viscosity profile. Thixotropy is an undesirable quality for tape- casting where, when a significant shear is applied, viscosity decreases and when left to stand the viscosity will increase. In other words, when the slurry is drawn under the blade, the viscosity will decrease, and upon casting, the viscosity increases preventing unnecessary flow and distortion of the sheet. Since thixotropy shows unstable behavior (which will result in poor thickness control), the sheets should be dried quickly in order to retain their shape. It should be noted that as the slurry experiences more shear stress with greater shear rate, granular and aticular particles can become oriented. A consequence of the orientation is the shrinkage rates in the x and y direction may be different and this effect can be demonstrated to a greater extent in thinner sheets.

[0071] Using a soft bake procedure, one may obtain a thin, flexible tape that can be cut and stamped to any desired configuration prior to firing. These green sheets comprise ceramic powder, binder (polymer materials, dispersing agents and plasticizers), and voids. It is desirable that the various ingredients are dispersed evenly and that the structure is homogeneous in the x, y, and z axes. From a macrostructure perspective, the thickness of the green sheet should be uniform (since the thickness of the green sheet will be the thickness of one layer in the MLD and this impacts the consistency of the end unit shape and performance). The green sheet should display minimal anisotropy, and there should be no macro defects such as scratches, cracks, blisters, or pin holes. The surface should have excellent smoothness, and it is desirable that there is no difference in the microstructure of the top and bottom of the sheet.

[0072] When leaving the green sheets to stand and when storing them it is desirable for dimensional changes and changes in characteristics to be kept to a minimum. If the dimensions change after the electrode pattern is printed on the surface of the green sheet or after blanking or punching (each discussed further below), the green sheet will not match those above and below in the MLD resulting in defects and the like. In addition, the green sheet should have the mechanical strength (hardness and elongation) to withstand the handling involved in each process. If the green sheet is removed from the carrier, the sheet may stretch or even break in some cases. Additionally, the cutting and punching processes can cause open or short circuits due to the shape of the holes formed. For this reason, sheets with good workability are needed, in which scraps do no stick to the sheets and in which the shape during processing can be kept close to that of the design. In the printing process, the surface of the sheet should show minimal surface roughness. Also, the conductive paste should have excellent adhesion to the sheet. After printing, the solvent in the ink should have good compatibility with the green sheet, penetrating and being absorbed without dissolution of the tape binder or blurring of the pattern. For lamination, the sheets should have elasticity and thermoplasticity. However, while the layers should adhere together, it is desirable that they do not distort any more than necessary.

[0073] The presently disclosed green tape technology also allows the possibility of fabricating three-dimensional ("3D") structures using multiple layers of green tapes. Each layer is fabricated in the green (before firing) with whatever features are needed for the overall function of the 3D structure. Each layer may have specific geometries, vias, and internal electrical elements (e.g., electrodes). The individual layers may be arranged (e.g., stacked) and placed in a registry to yield the desired structure. The location holes for registry and the vias may be punched, although they can additionally or alternatively be chemically dissolved, etched, abraded, or cut, in other embodiments.

[0074] As noted above, each of the green sheets may be punched, cut, and other machined to form a desired shape. Holes are often punched for alignment and via connections between layers. Punching and/or drilling may be used with numerical control ("NC"). Since there are hard ceramic particles mixed into the green sheets, abrasion of the tooling may occur readily, and wear charts should be utilized to maximize precision. Mechanical tooling can be applied to both via formation and shaping. As the green sheets are composed of ceramic particles and polymers, the shaping can additionally or alternatively occur through polymer degradation. By changing spot size and/or intensity of the laser, high precision x-y displacements and depth of penetration can be achieved. [0075] For the preparation of the cantilevers for biosensing, energy harvesting, and/or actuators, green sheets having the shapes illustrated FIG. 5 can be fabricated (by way of example). These designs can be extrapolated to accommodate any number of devices in an array configuration. The geometry of each cantilever can be identical (see middle diagram in FIG. 5) or can vary depending upon the application (see right diagram in FIG. 5). There is no fundamental limitation associated with the number of devices in an array configuration. Biosensors using an array of identical cantilevers can use one or more cantilevers as control groups. Biosensors using an array of cantilevers of varying geometries may be beneficial for targeting detection of particulates with varying sizes (proteins, viruses, bacteria, spores, oocytes, etc) because each cantilever will have a linear range of operation. Smaller cantilever devices will respond in a linear fashion for smaller particles, while larger cantilevers will have a linear dose response curve for larger particles. For multiple shape arrays, the configuration may include redundant shapes to serve as control/reference sensors.

[0076] For energy harvesters, the energy efficiency collected from external vibrations is dependent upon the applied frequency of the vibration and the resonant frequency of the energy harvester. By building an array of identical geometries, the device would generate the maximum amount of electrical energy in response to a fixed stimulation vibration. This is preferred if the external vibration is fixed or known, such as in a pump or motor, as it can be used to maximize energy collection, and also serve as a sensor for monitoring device function. In other words, if the energy harvesting power output response begins to drift, it could indicate the device is vibrating at a different frequency due to malfunction, etc. Alternatively, if the environmental conditions will change, and the frequency of the applied vibrations can vary, it would be beneficial to use an array of cantilevers with varying resonant frequencies to ensure energy can be generated under a wider range of applications.

[0077] The method 300 may also utilize screen printing (sometimes also referred to as gap printing) for printing electrodes, wiring patterns, and via filling on the green sheets. Screen printing is a technique in which a gap is set between the mask and the green sheet and, when a squeegee passes over the mask, the paste (or powder) is pushed through the opening in the mask onto the green sheet. Proper performance of the electrodes, wiring, and/or vias will depend upon print quality, including accurate positioning of the pattern, appropriate transfer ratio, and proper transfer shape)with stable/repeatable wet and dry thicknesses. This print quality will be impacted by screen specifications, printing process conditions, paste characteristics, and green sheet characteristics. The solution properties of the solvents in the paste should be considered so as to facilitate wetting, deter bleeding, and avoid damaging the underlying green sheet.

[0078] FIGS. 6 and 7 illustrate various embodiments of electrode patterns for MLDs.

The electrode patterns (cross hatched lines) on the punched green sheet (black, with white circles representing via holes) can run all the way to the edge of the cantilevers for complete coverage or, in other embodiments, may stop short of the edge. One advantage of using a pull- back is to prevent the paste from running over the edge and shorting the ceramic. An additional advantage is the ability to confine the application of the external field which can be used to improve the quality factor of the resonator. Bonding pads can also be deposited to facilitate external electrical connections. Two patterns may be utilized to indicate the top and bottom electrodes. In such embodiments, while the paste can be identical, the electrode patterns are differentiated to indicate that they will serve as opposing terminals (i.e., the top will be positive and the bottom will be negative, or the top can be negative and the bottom positive). The vias can be printed with a paste as well to serve as electrical conducts. The degree of filling can vary from a complete plug to coating a section of the walls. The degree of filling is dictated by sintering stresses and desired hermeticity.

[0079] The method 300 also involves laminating multiple green sheets to make a single substrate by aligning several layers of green tape on which the vias and printed circuit patterns have been formed. Stacking is the process of layering the sheets of green tape, and alignment is the process used to ensure that the circuit contacts in the three dimensional network make adequate connections. Alignment may be carried out using markers printed on the green tapes or holes punched in the green tape in conjunction with 4 CCD cameras and an x-y-angle stage. Pressure and heat may be applied and the layers of green tape to ensure each sheet sufficiently bonds to the sheets above and/or below it. Lamination can be carried out by stacking and aligning one sheet at a time, or multiple layers at one time. The pressure and heat can be applied using molds/fixtures with uniaxial and/or isostatic pressing. Care should be taken to ensure vertical splitting, surface blistering, stepped interlayer, circular, internal interlayer delamination do not occur during these processes.

[0080] Lamination may be used to build thickness for the MLD. However, lamination may also be used to control shrinkage, and minimize defects as the layers of tape can be rotated relative to one another as in building composites. Additionally, these techniques may be used to exploit the construction of a mechanical clamp. Using a higher modulus material such as a ceramic can improve the effect of the clamp. FIG. 8 illustrates one embodiment of layer green sheets of the same or different composition to clamp the cantilever device (horizontal lines).

The additional tape can be punched with vias to provide electrical connection to the external circuit, and laminated to build sufficient thickness to serve as a mechanical clamp.

Furthermore, these techniques can be utilized to extend the array into the vertical z-direction.

[0081] After the green sheets have been shaped and laminated, the 3D structure is ready for sintering (also sometimes referred to as firing or densification). In the sintering process, the porous green body undergoes a high temperature heat treatment, where significant atomic diffusion happens to eliminate pores and vacancies. In the case of a green tape by doctor blading, the binder may be burnt out completely below a temperature of 500°C, leaving a porous body for final sintering. The pores of a ceramic are usually closed, and the ceramic has

95% of theoretical density. For piezoelectric ceramics, densities below 95% usually display inferior properties because the presence of open pores allows for infiltration of water/humidity

(which increases dielectric loss and reduced volume resistivity). Dielectric strength may also be inferior for such densities, making it difficult (or impossible) to pole the ceramic. Sintering temperatures for piezoelectric ceramics are usually well above 1000° C.

[0082] Ceramic powders (co-precipitated, sol-gel derived, combustion, or Pechini derived) can be fused and densified through a variety of sintering methodologies including heat, pressure, electromagnetic radiation (e.g., microwave, IR), electric currents, or a combination of those processes. Liquid phase, reactive (transient liquid, and/or solid state) sintering techniques, in which the phase changes and chemical reactions between constituent phases take place during sintering process, may be utilized. Such techniques can be more advantageous than conventional calcination and sintering methods because of their simplified processing procedures and enhanced densification. Furthermore, the densification mechanisms described above can be used to reduce the energy input requirements for sintering, which allows for better control of the stoichiometry and microstructure. Finally, in addition to stoichiometry and microstructure, these techniques are capable of displaying repeatable shrinkage, and shrinkage rates, providing tight geometrical tolerances of the final sintered devices.

[0083] One challenged with MLD manufacturing is the choice of inner electrode composition. Interaction between ceramic and electrode may change the sintering behavior and final properties of the material; therefore, the reliability of the component also depends on this interaction. For lead zirconate titanate ("PZT"), platinum is an adequate electrode due to it inertness against reactions with PZT, which allows nearly unchanged sintering conditions and a free ceramic composition. Platinum, however is very expensive. Any material which will not react with the ceramic adversely, establishes similar thermal expansion, and can simultaneously sinter and shrink to the same degree as the ceramic (can be a blended with the host ceramic) can be utilized. Chemical and physical reactions may be exploited for the good bonding and mechanical strength of the interface ceramic electrode.

[0084] After sintering, additional metallization can be applied for soldering or wire- bonding. This additional metallization may facilitate the attachment of electrical connections of the device to the external electronics. Attachment of the device to external circuitry should be conducted in such a way that does not damage the device. During cooling at high temperature or soldering to substrate, larger thermal stress may be formed due to mismatched thermal expansion coefficients ("TEC"). The microcracks caused by the thermal stresses may become nuclei for crack propagation, especially during operation in an electric field. Mismatched contraction during cooling can make the metallization in the tensile state and the ceramic layer in the compressive state. The mismatch may be amplified by the rapid cooling rate, as electric power of the furnace suddenly stops at high temperature. The resultant shear stress at the interface may cause the formation of interfacial microdefects. At lower temperatures, although the cooling rate is slower, the mismatched TEC may still cause the production of interfacial cracks because of the reduced thermal relaxation effects compared to that under the condition of high temperature. Thus, a small TEC difference between the metallization and the ceramic should be employed for high-reliability MLD. After the metallization layers are patterned, deposited, and wires are attached, the devices can be enclosed in a housing unit to provide physical support and protection from damage while handling.

[0085] In many embodiments, the last step of the method 300 will be poling, in order to orient the ferroelectric domains. Grains in ferroelectric ceramics and polycrystalline films always contain multiple domains. Each domain has its own polarization direction. If the polarization directions through the material are random or distributed in such a way that it leads to a zero net polarization, the pyroelectric and piezoelectric effects of individual domains will cancel and such material is neither pyroelectric nor piezoelectric. Polycrystalline ferroelectric materials can be brought into a polar state by applying an adequate electric field. This process, which is referred to as poling, can reorient domains within individual grains in the direction of the field. The procedure for poling can vary depending upon the composition of the piezoelectric material, part design, and desired electrical properties. A poled polycrystalline ferroelectric exhibits pyroelectric and piezoelectric properties, even if many domain walls are still present.

[0086] While certain illustrative embodiments have been described in detail in the figures and the foregoing description, such an illustration and description is to be considered as exemplary and not restrictive in character, it being understood that only illustrative embodiments have been shown and described and that all changes and modifications that come within the spirit of the disclosure are desired to be protected. There are a plurality of advantages of the present disclosure arising from the various features of the apparatus, systems, and methods described herein. It will be noted that alternative embodiments of the apparatus, systems, and methods of the present disclosure may not include all of the features described yet still benefit from at least some of the advantages of such features. Those of ordinary skill in the art may readily devise their own implementations of the apparatus, systems, and methods that incorporate one or more of the features of the present disclosure.

Claims

WHAT IS CLAIMED IS:

1. A method of manufacturing a multilayer device, the method comprising:

tape casting a slurry comprising a ceramic powder and a binder to form a plurality of green sheets;

forming one or more of the plurality of green sheets into a desired shape;

depositing a circuitry pattern onto one or more of the plurality of green sheets;

laminating the plurality of green sheets with each green sheet at least partially overlapping at least one adjacent green sheet; and

cofiring the laminated plurality of green sheets to form the multilayer device.

2. The method of claim 1, wherein the tape casting comprises:

spreading the slurry to form a paste on a substrate; and

blading the paste to form a thin layer of slurry.

3. The method of claim 2, wherein the blading comprises drawing the paste under a blade to form the thin layer of slurry.

4. The method of claim 1, further comprising marking one or more of the plurality of green sheets for alignment.

5. The method of claim 4, wherein marking the one or more of the plurality of green sheets comprises forming location holes for alignment.

6. The method of claim 5, wherein forming the location holes comprises at least one of punching, dissolving, etching, abrading, and cutting the one or more of the plurality of green sheets.

7. The method of claim 1, wherein depositing a circuitry pattern comprises printing at least one of electrodes, wiring, and via fillings onto the one or more of the plurality of green sheets.

8. The method of claim 7, wherein the printing is screen printing.

9. The method of claim 1, wherein the laminating comprises aligning at least two of the plurality of green sheets.

10. The method of claim 9, wherein the aligning comprises stacking the at least two of the plurality of green sheets such that portions of the circuitry pattern on each of the at least two of the plurality of green sheets are connected with each other.

11. The method of claim 9, wherein the aligning is performed using charge coupled device (CCD) cameras and an x-y angle stage.

12. The method of any one of claims 1-11, wherein the laminating comprises applying pressure and heat to the plurality of green sheets to bond adjacent green sheets.

13. The method of any one of claims 1-11, wherein the laminating comprises cold isostatic pressing to increase green density.

14. The method of any one of claims 1-11, wherein the cofiring comprises burning out the binder at a temperature no greater than 500 °C.

15. The method of claim 14, wherein the cofiring comprises final sintering at a temperature of at least 1000 °C.

16. The method of any one of claims 1-11, wherein the cofiring comprises sintering by at least one of heat, pressure, electromagnetic radiation, and electric current.

17. The method of any one of claims 1-11, wherein the cofiring comprises sintering by at least one of liquid phase sintering and reactive sintering.

18. The method any one of claims 1-11, further comprising depositing metallization layers to complete electrical connections.

19. The method of any one of claims 1-11, further comprising poling the plurality of green sheets to orient ferromagnetic domains.

20. The method of claim 19, wherein the polling comprises applying an electric field to the plurality of green sheets.

21. The method of claim 1, wherein the ceramic powder is an ultrafine powder.

22. The method of claim 1, wherein the ceramic power is synthesized by a wet- chemistry-based processing route.

23. The method of claim 22, wherein the wet-chemistry-based processing route is one of chemical co-precipitation, sol-gel process, and hydrothermal reaction.

24. The method of claim 1, wherein the binder is a polymeric binder.

25. The method of claim 1, wherein slurry includes a solvent for dissolving the binder.

26. The method of claim 1, further comprising machining one or more of the plurality of green sheets to a desired dimension prior to the cofiring.

27. A multilayer cantilever preform comprising:

a preform stack including a plurality of sheets stacked together such that adjacent sheets at least partially overlap, each of the plurality of sheets comprising ceramic; and

a circuitry pattern arranged on one or more of the plurality of sheets;

wherein at least one cantilever arm is defined by at least a portion of the preform stack, the at least one cantilever arm including at least one piezoelectric layer and at least one non- piezoelectric layer.

28. The preform of claim 27, wherein one or more of the plurality of sheets includes a via hole defined though a thickness of the sheet.

29. The preform of claim 28, wherein a portion of the circuitry pattern extends through the via hole.

30. The preform of claim 29, wherein the portion of the circuitry pattern that extends through the via hole fills the via hole.

31. The preform of any one of claims 27-30, wherein the ceramic of the plurality of sheets has a theoretical density of at least 95% after burn out of a binder.

32. A multilayer cantilever green preform comprising:

a preform stack including a plurality of green sheets stacked together such that adjacent green sheets at least partially overlap, each of plurality of green sheets comprising ceramic and a binder dissolved in a solvent; and

a circuitry pattern arranged on one or more of the plurality of green sheets;

33. The preform of claim 32, wherein the binder has a glass transition temperature of 20 °C or less.

34. The preform of claim 32, wherein the solvent is free of volatile organic compounds (VOCs).

35. The preform of claim 32, wherein the solvent is free of hazardous air pollutants (HAPs).

36. The preform of any one of claims 32-35, wherein one or more of the plurality of green sheets includes a via hole defined though a thickness of the sheet.

37. The preform of claim 36, wherein a portion of the circuitry pattern extends through the via hole.

38. The preform of claim 37, wherein the portion of the circuitry pattern that extends through the via hole fills the via hole.