WO2015049598A1

WO2015049598A1 - Mems pressure sensor with a high electron mobility transistor and a production method thereof

Info

Publication number: WO2015049598A1
Application number: PCT/IB2014/063665
Authority: WO
Inventors: Gabriel VANKO; Jaroslav DZUBA; Tibor LALINSKÝ; Martin Vallo; Ivan RÝGER
Original assignee: Elektrotechnický Ústav Sav; Centrum Vedecko-Technických Informácií Sr
Priority date: 2013-10-02
Filing date: 2014-08-03
Publication date: 2015-04-09
Also published as: SK942013A3; SK288538B6

Abstract

MEMS pressure sensor with a high electron mobility transistor is construed so its circular or ring or "C"-shaped membrane is constituted by an active AlGaN/GaN hetero structure with an integrated C-HEMT sensing element with possible Si layer of the substrate, which contains at least one inner and one outer Schottky gate sensing electrode (1,2). The inner Schottky gate sensing electrode (1) is positioned to the radius (ri) of a ring sphere where the mechanical stress in the membrane changes its character from tensile to compressive or vice versa. The outer Schottky gate sensing electrode (2) is positioned above the radius (ri) of the ring sphere where the mechanical stress in the membrane changes its character from tensile to compressive or vice versa. Meanwhile, following relationship holds: ri = [ c+b / (hm+a) ]. rm -q, where: (hm) is a thickness of the membrane and (rm) is a radius of the membrane.

Description

MEMS pressure sensor with a high electron mobility transistor and a production method thereof

Field of technology

The invention concerns Micro-Electro-Mechanic System (MEMS) for measuring the external pressure on the basis of piezoelectric semiconductor material system AlGaN/GaN, which is also able to operate in extreme conditions of high temperature and chemically aggressive environment. The invention belongs to field of sensor technology and metrology.

State of the Art

Measuring pressure and mechanical tension belongs to the most significant application fields of Micro-Electro-Mechanic Systems (MEMS) exactly for the group of nitride semiconductor materials (III-N). It is caused by their excellent piezoelectric characteristics that are stable at high temperatures. Compared to other piezoelectric materials, they have multiple important advantages such as direct compatibility with high electron mobility transistors (HEMT) and high biocompatibility. Another advantage is the high mechanical stability of epitaxial layers which predetermines these materials for integration into multifunction Micro(Nano)-Electro-Mechanic Systems - M(N)EMS. Finally, it is the possibility to operate at high temperatures what is caused by their intrinsic capability to preserve their piezoelectric properties in vast range of temperatures. In general, AlGaN/GaN- based devices take advantage of the fact that piezoelectric polarization in AlGaN layer can be altered by externally applied forces. This alteration causes corresponding change in the density of the two-dimensional electron gas (2-DEG) localized on AlGaN/GaN heterointerface. This results in alterations in conductivity of HEMT directly related to the changes in external tension. Therefore, the HEMT transistors as well as Schottky diodes and AlGaN/GaN-based resistors can be used as sensor elements, especially when applied in harsh conditions of high temperatures and chemically aggressive environment (such as airplane wings, combustion engines, exhaust environment etc.).

In current state of the art, we have knowledge of piezo-response of these elements as pressure sensors either directly on volume element or in form of clamped membrane microstructures. The functionality of such sensors is provided by hydrostatic pressure which alters the Schottky potential barrier on the Ni/ AlGaN contact interface, the internal fields in the GaN/AlGaN/GaN heterostructure, and the polarization in AlGaN/GaN heterostructure. These effects are relatively small when compared with tension and pressure sensors which are exposed to direct bending (deformation). Sensor in this approach is sensitive to high pressures (~ kbar) and is also supported by high mechanical stability. The sensitivity of the sensor can be controlled by gate voltage and the highest sensitivity is achieved in the subthreshold region of the transistor.

In different solution of the pressure sensors, the process technology of the AlGaN/GaN HEMT is realized on volume substrates (sapphire A1₂0₃, silicon carbide SiC and silicon Si) with thickness in range of 200-300 μιη. The substrate with integrated HEMT sensor is cut into a macro-cantilever and after one-sided mechanical fix, exposed to a controlled mechanical bending stress. Such approach enables us to monitor the changes in 2-DEG channel resistance in relation to applied tension with greater sensitivity. The significantly higher sensitivity in piezo-response of AlGaN/GaN heterostructure as compared to piezoelectric SiC as well as GaN layers has been proved by acquired results. Mutual superposition of piezoresistance and piezoelectric effect of AlGaN/GaN heterostructure with localized 2-DEG on the given heterointerface significantly increases the sensitivity of pressure sensors.

In contrast with semiconductor material SiC, the potential of nitride group of semiconductors (III-N) as pressure sensors on the basis of membrane structures is much less presented. This is because of extremely complex process technology of clamped AlGaN/GaN membrane structures; especially if the heterostructure growth is realized on sapphire substrate material. Because of high chemical stability of SiC and/or sapphire, mainly the methods of surface micromachining employing sacrificial layers would be usable to fabricate membrane microstructures. However, realization of these methods is very difficult and highly sophisticated. More preferable approach is the growth of AlGaN/GaN heterostructure on Si as substrate material, when well-controlled conventional Si bulk micromachining techniques can be effectively used.

The above described problematic of pressure sensors is captured e.g. in document WO 2010022038, too. It includes a high electron mobility transistor (HEMT) which is capable of performing as a pressure sensor. Pressure sensor contains piezoelectric layer located at the gate area. Sensor contains aluminum gallium nitride (AlGaN)/gallium nitride (GaN) HEMT, aluminum gallium arsenide/gallium arsenide (GaAs) HEMT, indium gallium phosphide/GaAs HEMT, or indium aluminum arsenide/indium gallium arsenide HEMT.

Similar sensor for measuring pressures in harsh environments, measuring the internal pressure in combustion engine, is described in document EP 2477019. The sensor consists of an electronic circuit with high electron mobility transistors, which converts the detection of the change in shape of the membrane into an indication of a magnitude of the pressure. The membrane is a part of the substrate. There is a GaN layer on the substrate with an AlGaN layer deposited on the top of this GaN and 2-DEG is created at their interface. The Schottky gate contact is patterned on the top of Si0₂ or A1₂0₃ passivation layer.

Above described proposals of pressure sensors with high electron mobility transistors suggested creation of such MEMS pressure sensor for measuring of external pressure on the basis of piezoelectric, semiconductor AlGaN/GaN material system. In addition, it is able to operate in extreme conditions of high temperature or chemically aggressive environment, intending to maximize the sensing of the value of the charge and therefore, increasing the sensitivity of the sensor. It is preferable that the good characteristics of AlGaN/GaN-based sensors, such as high temperature resistance and good performance in a harsh environment, are taken advantage of, and yet the sensitivity is increased at the same time. This results in construction solution of MEMS pressure sensor with the high electron mobility transistor described further; further described is also a method of production of such.

Subject matter of the invention

The abovementioned deficiencies are remedied by a solution of MEMS pressure sensor with a high electron mobility transistor and the method of its production. Towards this purpose the C-HEMT - Circular High Electron Mobility Transistor with circular topology of Schottky gate sensing electrodes integrated on circular, ring or "C"-shaped membrane created either by active AlGaN/GaN heterostructure of C-HEMT on the Si substrate or by active AlGaN/GaN heterostructure of C-HEMT without Si substrate, is used. After the connecting of materials with different bandgap (AlGaN, GaN)by method of epitaxial growth, a thin layer of electrons, also known as 2-DEG - 2-Dimensional Electron Gas, is created at their interface as result of different spontaneous polarization between AlGaN and GaN and piezoelectric polarization in the AlGaN layer. The 2-DEG is fixed in triangular quantum well created on the interface of the two mentioned layers. In this way, the electrically conductive channel of the HEMT is created. By application of mechanical force the amount of piezoelectric polarization of AlGaN is altered. This results in perturbation of the steady-state concentration of charge. In the piezoelectric AlGaN layer, an additional charge is generated which also contributes to the concentration of 2-DEG and therefore alters the total conductivity of the transistor's channel. In principle of the sensing according to this invention, only the charge change generated in the AlGaN layer is used. It means that the transistor operates in the function of vertical, capacitor, where the lower electrode comprises of the conductive 2-DEG channel electrically and conductively connected to ohmic contacts of the HEMT (source-drain electrodes) while the Schottky gate electrode is in the function of the upper electrode. The generated charge is directly proportional to external dynamic exciting force and it is independent of exciting frequency. The amount of generated charge can be tuned by tuning the area of Schottky gate sensing electrode.

Solution of MEMS pressure sensor according to this invention consists in arranging of the C-HEMT sensing element as a circularly symmetrical HEMT functioning as piezoelectric pressure sensor directly onto thin circularly symmetrical or asymmetrical AlGaN/GaN membrane, on which the pressure change will be applied and subsequently the amount of generated charge will be measured on at least two Schottky gate sensing electrodes. The important factor when designing a sensor is also the residual stress built in the AlGaN/GaN layer and therefore in the membrane, too. The important feature of this solution is also maximal possible dimensions of membrane, when the cracking or disturbing the membrane due to built-in tension is avoided. In this way, the highest value of generated charge is achieved. In this solution, two Schottky gate sensing electrodes are used because the distribution of the charge on the surface of the membrane is not constant but it changes with regard to the character of the mechanical tensile or compressive stress in the membrane; additionally, the +/- sign of the charge changes, too. Covering the entire surface of the membrane by one Schottky gate sensing electrode causes an unwanted charge loss what is a consequence of the charge compensation due to influence of opposite signs. This is why in solution according to this invention the crucial feature is solution with inner and outer Schottky gate sensing electrode. These electrodes are located in optimal locations on the membrane surface, in order to maximize the amount of the charge as well as the sensitivity of the pressure sensor.

It is obvious, that by moving the inner Schottky gate sensing electrode from the middle of the membrane towards its outer edge, the electrode area increases and therefore, theoretically, the measured amount of sensed charge within single polarity should increase. This happens until certain radius is achieved. Critical radius is located in place, where the inner Schottky gate sensing electrode moves to the location where the character of mechanical stress in membrane changes. The position of this place (that is the radius of a toroidal sphere of the change of the character of the mechanical tensions) depends on the parameters of the membrane that are the diameter of membrane and the thickness of the membrane, according to functional dependence:

ri = [ c + b / ( h_m + a ) ] . r_m - q,

where: r_m ... is the membrane radius, h_m ... is thickness of the membrane,

a ... is first material constant of the membrane,

b ... is second material constant of the membrane,

c ... is third material constant of the membrane,

q ... is shift.

At this critical point (also called singular point or zero stress point or neutral stress line), the mechanical stress changes its character, that is, from tensile to compressive or vice versa, and so the measured piezoelectric charge changes its polarity. In case of a circular membrane the neutral stress line has the shape of a circle. Other membranes can have a differently shaped neutral stress line; the shapes can be determined either by analytical computation, or by measuring by means of the known measuring methods. It is not worth patterning a Schottky gate sensing electrode with location and surface area over these two different areas because induced piezoelectric charge would compensate itself due to different polarities. The interesting phenomenon is the dependency of induced charge on the surface area of the Schottky gate sensing electrode. The value of charge should increase with increasing the surface area but changes in distribution and character of the mechanical stress in the membrane cause the decreasing of charge to surface area ratio (i.e. charge yield) for Schottky gate sensing electrode with regard to the position of this electrode on the top of the membrane. By dimensioning the C-HEMT transistor, a sufficient sensitivity to the applied external pressure can be observed what means that adequate mechanical deflection of the membrane can be obtained. Dimensioning includes the masks of circular and ring membranes with different diameters ranging from 700 μπι to 2000 μπι, but also with smaller and bigger diameters and also a specific position of Schottky gate sensing electrodes. The width and surface area of the Schottky gate sensing electrodes are also reflected in the dimensioning. Membranes of some proposed structures are covered by two Schottky gate sensing electrodes at the same time i.e. electrodes, that are patterned only as sequential parts of rings with two different positions, while the structure is divided in two halves and each of Schottky gate sensing electrodes is located only in one of these halves within the structure, that is, inner Schottky gate sensing electrode is located to the neutral stress line and the outer Schottky gate sensing electrode is located above the semidiameter of the neutral stress line. Membranes of other proposed structures are covered simultaneously by two Schottky gate sensing electrodes, that is by electrodes that are patterned as whole rings with two different positions, while the inner Schottky gate sensing electrode has the ring shape with its defined width of the ring and the outer Schottky gate sensing electrode also has the ring shape with its defined width of the ring. In both alternate solutions the expanded bonding contacts of the inner and outer Schottky gate sensing electrodes are led out of the circular membrane region.

Weak temperature dependency of piezoelectric constants of above mentioned semiconductors allows realizing temperature independent HEMT based piezoelectric pressure sensors without need of subsequent mechanism of heat compensation. Excellent electronic, mechanical and thermal- properties of the abovementioned heterostructure allow solving the concept of proposal of MEMS pressure sensors on the basis of remote wireless sensing in extreme conditions of high temperatures and highly corrosive environment.

A method of production of the MEMS pressure sensor with high electron mobility transistor is characterized in such a way that Schottky gate sensing electrodes are patterned after etching the MESA type isolation island, or they are patterned before the isolation layer is applied and then the etching of the substrate intended for production of circular or ring membrane follows. In the first method of production on the basis of MESA isolation the AlGaN layer is etched in places outside of mutually independent Schottky gate sensing ring electrodes with delimited sequential ring surface area. In second method of production on the basis of isolation layer, the deposition of thin isolation layer on the whole surface of the sensor is performed after patterning the whole ring Schottky gate sensing electrodes with selective etching of the holes in the isolation layer before the deposition of the upper contact metallization by shaping the expanded contacts for bonding, whereby the isolation layer is S13N4 or S1O2 or other commonly used isolation layers.

The advantages of the MEMS pressure sensor with high electron mobility transistor and the method of its production result from its overall behavior. That means they can be applied in extreme conditions of high temperature or chemically aggressive environment. Another important advantage is the high temperature stability of piezoelectric properties, which is set by Curie temperature above 1000°C, whereby the functioning of HEMT is conditioned in high temperature environments. The membrane or cantilever micro-machining with excellent thermal and mechanical stability, usable in MEMS pressure sensor designing is realized thanks to the excellent mechanical properties of AlGaN/GaN semiconductor caused by high Young's modulus (E₀=310GPa) which is thermally independent up to T-1000 K. The advantage also lies in longer lifetime of the MEMS pressure sensor as compared to commonly used pressure sensors in extreme conditions what is lowering the production costs. Another advantage of the MEMS pressure sensor according to this invention is a considerable increase in sensitivity compared to other sensors made of the same materials. Moreover, the integration of the sensor and control electronics on a single board (chip) is possible what allows a direct installation of the sensor to the measured environment (place of interest) and a wireless transfer of the energies and signals. The MEMS pressure sensor according to this invention has the excellent piezoelectric characteristics thanks to the usage of semiconductor GaN material system. Finally, the extreme sensitivity of AlGaN to any changes in the static but mainly dynamic stress allows to sense and detect the pressure applied on the membrane initiated hydrodynamically, acoustically, or by acceleration.

Description of the drawings

The construction solution of MEMS pressure sensor with high electron mobility transistors is depicted on attached drawings, where fig. 1 depicts the shape and localization of whole inner ring and whole outer ring Schottky gate sensing electrode. Fig. 2 depicts the localization of inner sequential ring and outer sequential ring Schottky gate sensing electrode. Radius ri in the figures 1 and 2 (for the sake of clarity the radius is not explicitly drawn in these figures) is between the outer radius of the circle 1 and the inner radius of the ring 2. Fig. 3 depicts a dependency of simulated piezoelectrically induced charge on the position of Schottky gate sensing electrode on the circular membrane. From the membrane center (0) to radius of 60 μπι, the source electrode of the HEMT is positioned on the surface of membrane. The curve represents the dependency of the charge on the position of Schottky gate sensing electrode. Two hatched rectangles denote the space for preferable location of the two Schottky gate sensing electrodes and crosshatched rectangles represent a space where the substrate is located. Fig. 4 shows a dependency of the charge yield (Q/A) on the position of Schottky gate sensing electrode located on the circular membrane. By increasing the outer radius of electrode r₂₂, that is, by increasing its radial distance from the membrane center (i.e. radial position), the surface of the Schottky electrode increases naturally. Nevertheless, the charge does not increase proportionally to the surface of the Schottky gate sensing electrode. The graph in fig. 5 depicts a dependency of the membrane radius r_m and the radius n of the ring sphere where mechanical stress changes its character from tensile to compressive or vice versa, while the thickness of circular membrane h_m is the parameter. The graph in fig. 6 depicts a change in slope of the parametric straight line in dependence upon the thickness h_m of the circular membrane for determining the radius n of the circular neutral stress line dependent on the membrane radius. In fig. 7, there is a flow chart of the process technology of the MEMS pressure sensor based on MESA isolation. Fig. 8 shows a flow chart of the process technology of the MEMS pressure sensor based on the isolation layer.

Examples

Following examples of the realization of the invention are meant for illustration and are not meant as limitation of technological solutions. A person skilled in art will be able - using no more than routine experimentation - to find many equivalents to specific realizations of the invention as described. These equivalents fall within the scope of the protection of the following patent claims.

For a person skilled in art, it can present no problem to dimension such device and to choose adequate materials and construction arrangements; this is why these matters are not tackled in detail.

Obviously, there can be more modifications of the solutions which fall within the essence and gist of this invention.

Example 1

Solution of the MEMS pressure sensor with high electron mobility transistor according to this invention will be hereby in this example presented by following description and it is depicted in fig. 1. In case of MEMS pressure sensor with circular membrane with radius = 1000 μπι, the radius £_j of the neutral stress line is located circa 950 μπι from the middle of the membrane running to its outer edge. Therefore, it is located almost at the place where the membrane is clamped to the substrate as depicted in the fig. 3. It is based on the following relationship:

ri = [ c + b / ( h_m + a ) ] . r_m - q; when we fill in the concrete values:

ΐϊ = [ 0,28 + 32,37 / ( 2,645 + 44,47 ) ] . 1000 - 17 = 950,04 μιη.

The source electrode 5 of the transistor with its expanded contact electrode 7 already located in the center of the membrane. To prevent electrical shortening with this source electrode ^ the inner ring Schottky gate sensing electrode cannot be located at this place. The smallest radius of this inner ring Schottky gate sensing electrode 1 is the radius of the source electrode 5 plus few micrometers of distance because of leaving the minimal gap between the electrodes. This minimal gap depends upon the maximal resolution of the processing technology with regard to the patterning the electrodes of the MEMS pressure sensor. The largest radius of the inner ring Schottky gate sensing electrode I equals automatically to the radius r_j of the neutral stress line. With regard to these facts, the preferable radiuses of the inner ring Schottky gate sensing electrode I will be: inner radius rn > 70 μιη and outer radius ri₂≤ 950 μιη. The inner ring Schottky sensing electrode I will have the ring width of hgi = 880 μιη. The outer ring Schottky gate sensing electrode 2 is proposed to measure induced charge of opposite polarity in the places with opposite character of the mechanical stress in the membrane. The following radiuses are preferable for the outer ring Schottky gate sensing electrode 2: inner radius of £₂₁ > 950 μιη and outer radius of £₂₂≤ 1050 μιη. Outer ring Schottky gate sensing electrode 2 will have the width of the ring of = 100 μιη.

The MEMS pressure sensor with high electron mobility transistor according to this invention is manufactured as it is schematically depicted in fig. 8. This particular method of manufacturing of MEMS pressure sensor is on the basis of isolation layer - deposition of a thin S13N4 isolation layer on the whole surface of the sensor after the patterning of Schottky gate sensing electrodes. The circular membrane is created by etching the cylindrical volume into the Si substrate in the last technological step. The disadvantage of the method on the basis of isolation layer is the need of other step in the process; the step of the selective etching of windows in the isolation layer S13N4 prior to the deposition of the upper contact metallization (patterning the expanded contacts). Its advantage is, however, that whole ring surface area of both gate sensing electrodes can be used.

More in depth description of the production of MEMS pressure sensor with high electron mobility transistor lies in the production of:

- A - ohmic contacts (source-drain electrodes) - their production includes two steps: (a) electron beam evaporation of thin Nb, Ti, Al, Ni metal layers and conventional thermal evaporation of Au metal layer and subsequent patterning by lift-off technique, (b) alloying with the use of rapid thermal annealing (RTA - Rapid Thermal Annealing) in nitrogen atmosphere;

- C - Schottky contacts (gate electrodes) - the preparation consists in two steps (because here we consider gates with high thermal stability): (a) deposition of thin Ir metal layer prepared by electron beam evaporation and subsequent lift-off patterning technique; (b) formation of thermally stable conductive Ir0₂ metal oxide layer using of rapid thermal annealing in the oxygen atmosphere;

- F - isolation layer - this layer is prepared by low pressure chemical vapor deposition and this layer serves as an electrical insulation of Schottky gate electrodes from the upper contact metallization. Therefore, windows (openings) for upper contacts are etched into this layer after its deposition; - D - upper contacts - the preparation constitutes of electron beam evaporation of a thin Ir/Au metal layer and subsequent lift-off patterning technique;

- E - etching of the substrate - by using a technique of deep (bulk) selective reactive ion etching with assistance of inductively coupled plasma (ICP DRIE). The first layer (ΑΓΝ or GaN) grown on Si serves as etching-stop layer in the process of bulk Si micromachining.

Alternatively, the MEMS pressure sensors with high electron mobility transistor according to this invention, with ring membrane, can be produced.

Further alternative is production of MEMS pressure sensors with high electron mobility transistor according to this invention, where the circular membrane can be produced by etching a certain depth of cylindrical volume in Si substrate in either last or primary technological step.

Further alternative is production of MEMS pressure sensors with high electron mobility transistor according to this invention, where Si0₂ isolation layer is used.

Example 2

This solution of MEMS pressure sensor with high electron mobility transistors according to this invention will be presented by following description and it will be depicted in fig. 2. In case of MEMS pressure sensor on the circular membrane of = 1000 μπι radius, the radius £_j of the neutral stress line is circa 950 μπι from the middle of the membrane towards to its outer radius, therefore almost in the place where the membrane is clamped to the substrate, as depicted on the fig. 3.

In the middle of the circular membrane the source electrode 5 of the transistor is located. The smallest radius of inner sequential ring Schottky gate sensing electrode I can therefore be the radius of source electrode 5 plus few micrometers of distance because of the minimal gap between electrodes. This minimal gap depends upon the maximal resolution of the processing technology with regard to the patterning the electrodes of the MEMS pressure sensor. The largest radius of the inner sequential ring Schottky gate sensing electrode 1 is automatically a radius r_j of the neutral stress line. With regard to these possibilities, the preferable radius of the inner ring Schottky gate sensing electrode I will be: inner radius rn > 70 μπι and outer radius ri2≤ 950 μπι. For the purposes of inner sequential ring Schottky sensing electrode I we need to understand the term "sequential ring" as a part of the ring, in this particular case the ring sector of circa 110° with the width of the ring of hgi = 880 μπι. The outer ring Schottky gate sensing electrode 2 is proposed to measure induced charge of opposite polarity in the places with opposite character of the mechanical stress in the membrane, where the membrane is attached to the drain electrode 6 of the substrate. The following radiuses are preferable for the outer sequential ring Schottky gate sensing electrode 2: inner radius of £21 > 950 μιη and outer radius of £22≤ 1050 μιη. For the purposes of outer sequential ring Schottky sensing electrode 2 we need to understand the term "sequential ring" as a part of the ring, in this particular case the ring sector of circa 160° with the width of the ring of h i = 100 μιη.

This MEMS pressure sensor with high electron mobility transistor according to this invention is produced as it is schematically depicted in fig. 7. This particular method of production of MEMS pressure sensor is on the basis MESA isolation - etching of the AlGaN layer in places outside ring Schottky gate sensing electrodes. By this method, the gate electrode is effectively isolated from the other electric components. By this method, it is possible to integrate multiple mutually independent gate sensing electrodes of the transistors on the membrane but with limited "sequential" ring surface. The circular membrane is produced by etching the whole cylindrical volume in Si substrate in the last technological step. Its disadvantage is a smaller surface and lower value of measured charge.

More in depth description of the production of MEMS pressure sensor with integrated high electron mobility transistor lies in the production of:

- B - MESA isolation - this means the etching of the thin AlGaN barrier layer through to the lower GaN layer (circa 100 nm in total) by using a technique of reactive ion etching (RIE) in chlorine plasma; by doing so the size and shape of the transistor is determined and the electrons will flow only in the transistor channel in exactly defined space;

- D - upper contacts - the preparation constitutes of electron beam evaporation of a thin Ir/Au metal layer and subsequent lift-off patterning technique; - E - etching of the substrate - by using a technique of deep (bulk) selective reactive ion etching with assistance of inductively coupled plasma (ICP DRJE). The first layer (ΑΓΝ or GaN) grown on Si serves as etching-stop layer in the process of bulk Si micromachining.

Alternatively, the MEMS pressure sensors with high electron mobility transistor according to this invention, with ring membrane can be produced.

Industrial applicability

The MEMS pressure sensors with high electron mobility transistor according to this invention can be used in extreme conditions with high temperatures.

List of related symbols

1 - inner ring Schottky gate sensing electrode;

2 - outer ring Schottky gate sensing electrode;

3 - contact of the inner Schottky gate sensing electrode

4 - contact of the outer Schottky gate sensing electrode

5 - source electrode

6 - drain electrode

7 - contact electrode

Claims

P A T E N T C L A I M S

MEMS pressure sensor with a high electron mobility transistor is characterized by the fact that a circular or ring or "C"-shaped membrane is constituted by an active AlGaN/GaN heterostmcture with a C-HEMT sensing element, which contains at least one inner and at least one outer Schottky gate sensing electrode (1, 2), whereby the inner Schottky gate sensing electrode (1) is positioned inside a surface of a delimited neutral stress line and the outer Schottky gate sensing electrode (2) is positioned outside, beyond the neutral stress line, preferably in a case of the circular membrane the inner Schottky gate sensing electrode (1) is positioned inside the radius (ri) of a circular neutral stress line and the outer Schottky gate sensing electrode (2) is positioned beyond the radius (ri) of the circular neutral stress line.

MEMS pressure sensor with the high electron mobility transistor according to claim 1 is characterized by the fact that the circular or ring or "C"-shaped membrane is constituted by the active AlGaN/GaN heterostmcture of the C-HEMT sensing element with a layer of a Si substrate.

MEMS pressure sensor with the high electron mobility transistor according to claims 1 to 2 is characterized by the fact that the radius (ri) of a ring sphere where the mechanical stress in the membrane changes its character from compressive to tensile or vice versa is a function of a thickness (h_m) and a radius (r_m) of the membrane according to relationship:

ri = [ c + b / ( h_m + a ) ] . r_m - q

where: a ... is a first material constant of the membrane;

b ... is a second material constant of the membrane;

c ... is a third material constant of the membrane;

q ... is a shift.

MEMS pressure sensor with the high electron mobility transistor according to at least one of the claims 1 to 3 is characterized by the fact that the inner Schottky gate sensing electrode (1) is ring-shaped with a width of a ring (h_pi) and outer Schottky gate sensing electrode (2) is ring-shaped with a width of a ring (h_p2).

MEMS pressure sensor with the high electron mobility transistor according to at least one of the claims 1 to 3 is characterized by the fact that the inner Schottky gate sensing electrode (1) is positioned on one half of the circular or ring or "C"-shaped membrane with the width of the ring (h_pi) by a sequential part of the ring and outer Schottky gate sensing electrode (2) is positioned on the other half of the circular or ring or "C"-shaped membrane with the width of the ring (h_p2) by a sequential part of the ring.

6. MEMS pressure sensor with the high electron mobility transistor according to at least one of the claims 1 to 5 is characterized by the fact that the contacts (3) of the inner Schottky gate sensing electrode (1) and the contacts (4) of the outer Schottky gate sensing electrode (3) are led outside the circular or ring or "C"-shaped membrane.

7. A method of production of MEMS pressure sensor with a high electron mobility transistor with technological steps consisting of a creation of the ohmic contacts and expanded top contacts, is characterized by the fact that the Schottky gate sensing electrodes are produced after MESA-type isolation etching or before application of an isolation layer.

8. The method of production of MEMS pressure sensor with the high electron mobility transistor according to claim 7 is characterized by the fact that before production or after production of the Schottky gate sensing electrodes a whole or partial etching of the substrate for production of a circular or ring or "C"-shaped membrane follows.

9. The method of production of MEMS pressure sensor with the high electron mobility transistor according to claims 7 and 8 is characterized by the fact that a thin AlGaN barrier layer is etched on the basis of MESA isolation outside the places where the multiple mutually independent ring Schottky gate sensing electrodes with a delimited sequential ring surface are patterned.

10. The method of production of MEMS pressure sensor with the high electron mobility transistor according to claims 7 and 8 is characterized by the fact that a deposition of a thin isolation layer on the whole surface of the sensor takes place on the basis of the isolation layer after the patterning of the whole ring Schottky gate sensing electrodes with a selective etching of the windows in the isolation layer before the deposition of an expanded top contact metallization.

11. The method of production of MEMS pressure sensor with the high electron mobility transistor according to claims 7, 8 and 10 is characterized by the fact that the isolation layer is S13N4 or Si0₂.