WO2013166133A1

WO2013166133A1 - Thermal imaging system including an actuator

Info

Publication number: WO2013166133A1
Application number: PCT/US2013/039042
Authority: WO
Inventors: Howard Beratan; S. S. N. Bharadwaja
Original assignee: Bridge Semiconductor Corporation
Priority date: 2012-05-02
Filing date: 2013-05-01
Publication date: 2013-11-07

Abstract

In a thermal imaging system and method of using the thermal imaging system, a piezoelectric actuator is disposed between a thermal sensor and a readout circuit. Total radiance in the scene is detected with the thermal sensor and background radiance in the scene is detected by movement of at least a portion of the piezoelectric actuator between the thermal sensor and the readout circuit. The detected background radiance is subtracted from the detected total radiance to provide a signal representing the actual radiance of an object in a scene.

Description

THERMAL IMAGING SYSTEM INCLUDING AN ACTUATOR

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U.S. Provisional Patent Application No. 61/641,414, filed May 2, 2012, which is incoiporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] Field of the Invention

[0003] This invention is related to a thermal imaging system including an actuator for detecting thermal radiance of objects in a scene.

[0004] Background

[0005] In various infrared or thermal imaging systems, thermal sensors are utilized to detect infrared radiation (e.g., radiation in the 7μιη to 14μηι band) and generate an image suitable for viewing by the human eye. Such systems detect small thermal radiation differences emitted by objects in a scene and convert the differences into electrical charges which tend to be extremely small. The electrical charges are then conditioned to produce related electronic signals. Such conditioning may include amplification, noise-correction, filtering, etc. However, amplifying the electric charges to a suitable level often produces undesirable consequences such as increased noise, weaker signal-to-noise ratios, etc.

[0006] The radiation detected by the thermal sensors includes a direct current (DC) component and an alternating current (AC) component. The DC component is an offset that is generated by the background radiation, whereas the AC component is derived from radiance differences emitted by objects within the scene. The AC component is generally quite small compared to the DC component. In order to generate a satisfactory visual image from the detected radiation, various scene artifacts need to be minimized. What is needed are improved sensors and methods which can accommodate artifacts.

SUMMARY OF THE INVENTION

[0007] Disclosed herein is a thermal imaging system comprising a thermal sensor; a readout circuit in spaced relation to the thermal sensor and a piezoelectric actuator coupled to the readout circuit and under the control of the readout circuit for causing a portion of the piezoelectric actuator to move from a first state spaced from the themial sensor to a second state either in contact with the themial sensor or in closer proximity to the themial sensor than the first state and vice versa.

[0008] The portion of the piezoelectric actuator can include a tip. The readout circuit can apply a voltage to the piezoelectric actuator that causes the piezoelectric actuator to move from the first state to the second state or vice versa. [0009] The themial sensor can comprise at least one pixel. Each pixel can include electrical interconnects that connect the pixel to the readout circuit and which maintain the readout circuit in spaced relation to the pixel.

[0010] The pixel elements can be formed from pyroelectric material.

[0011] The piezoelectric actuator can be one of the following: a unimorph actuator, a bimorph actuator, or a multimorph actuator. The piezoelectric actuator can have one of the following configurations: a d31 configuration or a d33 configuration.

[0012] The system can comprise a plurality of thermal sensors and a plurality of piezoelectric actuators.

[0013] The plurality of thermal sensors and a plurality of piezoelectric actuators comprise a 160X120, a 320X240, or 640X480 focal plane array.

[0014] The piezoelectric actuator can be spiral shaped or can be in the shape of a beam.

[0015] Also disclosed herein is a method of detecting radiance of objects in a scene, comprising: a) providing a themial imaging system comprising a piezoelectric actuator disposed between a themial sensor and a readout circuit; b) detecting total radiance in the scene with the thermal sensor; c) detecting background radiance in the scene by movement of at least a portion of the piezoelectric actuator between the thermal sensor and the readout circuit; and d) subtracting the background radiance detected in step (c) from total radiance detected in step (b) to provide a signal representing radiance of objects in a scene.

[0016] The movement of the actuator can include either touching the sensor or not touching the sensor. The movement of the actuator can include the actuator in contact with the thermal sensor and the readout circuit.

[0017] The actuator can operate in resonance mode or in off-resonance mode. The actuator can include a duty cycle.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Fig. 1 is a high-level block diagram of a themial imaging system in accordance with the present invention;

[0019] Fig. 2 is a side view of a themial imaging system including a first embodiment actuator in a first position;

[0020] Fig. 3 is a view of the thermal imaging system of Fig. 2 with the first embodiment actuator in a second position;

[0021] Fig. 4 is a plan view of the thermal imaging system shown in Figs. 2 and 3;

[0022] Fig. 5 is an isolated plan view of the first embodiment actuator shown in Fig. 2; [0023] Fig. 6 is a side view of a thermal imaging system including a second embodiment actuator in a first position;

[0024] Fig. 7 is a view of the thermal imaging system of Fig. 6 with the second embodiment actuator in a second position; and

[0025] Fig. 8 is an isolated plan view of the second embodiment actuator shown in Fig. 6.

DETAILED DESCRIPTION OF THE INVENTION

[0026] It is to be understood that at least some of the Figs, and descriptions of the invention have been simplified to illustrate elements that are relevant for a clear understanding of the invention, while eliminating, for purposes of clarity, other elements that those of ordinary skill in the art will appreciate may also comprise a portion of the invention. It will also be understood by those having ordinary skill in the art that when a layer or element is described herein as being "on" another layer or element, it may be formed directly on the layer, at the top, bottom or side surface area, or one or more intervening layers may be provided between the layers.

[0027] Fig. 1 illustrates a high-level representation of an embodiment of an imaging system 10. The system 10 may be a thermal imaging system used to thermally capture a thermal scene and generate a signal that is representative of the scene. In some embodiments, the signal may be translated into an image that is suitable for viewing by the human eye. In another embodiment, the system 10 includes a sensor 12, an actuator 14 and a portion of a readout integrated circuit (ROIC) 16 housing the pixel-level circuitry. As used herein, the term "sensor" means an element comprising 1) a pixel comprising a thermally sensitive material; 2) electrical interconnects (electrodes) for connecting the pixel to a readout circuit; and 3) a structure or structures for providing thermal isolation of the pixel.

[0028] The sensor 12 is electrically connected to the ROIC 16, and may be embodied as any suitable type of thermal sensor. In some embodiments, the thermally sensitive material is a thin-film pyroelectric material. Examples of suitable pyroelectric materials include lead zirconate titanate (PZT), barium strontium titanate (BST), barium titanate (BT), antimony sulfoiodide (SbSI), lead lanthanum titanate (PLT), lead titanate (PT), lead lanthanum zirconate titanate (PLZT), lead zinc niobate (PZN), lead strontium titanate (PSrT), lead scandium tantalate (PST), and doped versions of any of these, such as manganese doped PZT (Mn:PZT) and manganese doped PLT (Mn:PLT). Other types of thermal sensors, such as micro bolometers, can also be used in the thermal imaging systems of the invention.

[0029] The actuator 14 is in contact with the ROIC 16, and as described in more detail herein below, may also be in contact with the pixel at various times (this is shown as a dashed line in Fig. 1). Desirably, the actuator 14 is a piezoelectric actuator configured to extend from a first position to a second position when a sufficient voltage/electric field is applied to it. The first position may be considered an "at rest" position which is shown in Fig. 2 and the second position may be considered a "fully extended" position, shown in Fig. 3. When in the fully extended position, the actuator 14 is in contact with both the sensor 12 and the ROIC 16, and operates as a thermal shunt between the sensor 12 and the ROIC 16. Under certain circumstances, such as intrinsic thin film stress imbalance conditions, the actuator can be positioned at rest by means of external direct current (DC) voltage. During thermal shunting, the DC voltage is removed and the actuator touches the bottom part of the pixel.

[0030] The piezoelectric actuator 14 may be embodied as a microelectromechanical device having a unimorph configuration, a bimorph configuration, or a multimorph configuration, and may operate in either the d31 mode or the d33 mode. Depending upon the ROIC drive circuit, either d33 or d31 mode of operation will be used.

[0031] For example, in some embodiments, the piezoelectric actuator 14 may be fabricated in a unimorph configuration (d33 mode), and it will comprise a single active layer and a single inactive layer. In other embodiments, such as in a bimorph configuration, the piezoelectric actuator 14 may be fabricated to comprise two active layers separated by an inactive layer. In additional embodiments, the actuator 14 may have a multimorph configuration, with multiple active layers. Deformation in the active layer may be induced by the application of an electric field.

[0032] The active layer (in any configuration) may comprise a thin film piezoelectric material, such as aluminum nitride (AIN), doped AIN, for example using dopants such as scandium, Zn, Sm, holmium or thulium or other dopant; or modified lead zirconate titanate, for example PZT that has been modified with donor dopants such as lanthanum (La), niobium (Nb), samarmm(Sm), manganese (Mn) and combinations of these. For low power applications, the piezoelectric material may be acceptor doped with materials like Al or Fe. Additional suitable piezoelectric materials include, for example, zinc oxide, gallium arsenide, aluminum gallium arsenide, gallium nitride, quartz, zinc-sulfide, cadmium-sulfide, lithium tantalate, lithium niobate, and other members of the lead lanthanum zirconate titanate and ferroelectric relaxor families.

[0033] The inactive layer, also referred to herein as the strain layer, can comprise a silicon oxide (SiOx), for example Si0₂, or silicon nitride (Si₃N₄ or SiN_x).

[0034] The actuator 14 will also include an upper and a lower electrode. The upper electrode will comprise a material that is reflective in the IR region and is also highly thermally conductive. Examples of suitable materials for the reflective electrode include aluminum (Al), titanium aluminide (TiAl), titanium aluminum nitride (TiAIN) or titanium nitride (TiN). Additional suitable reflective conductive materials include platinum, molybdenum, tungsten, titanium, niobium, ruthenium, chromium, doped polycrystalline silicon, doped AlGaAs compounds, gold, copper, silver, tantalum, cobalt, nickel, palladium, silicon germanium, doped conductive zinc oxide, and combinations of any of these. In various implementations, the upper metal electrodes and/or the lower metal electrodes can comprise the same conductive material(s), or they can be different conductive material(s). It is not required that the bottom electrode be reflective. The reflective layer may comprise the "top" portion of the actuator 14 that comes into contact with the pixel when the actuator 14 is in the second position, and may also comprise other portions of the actuator 14.

[0035] In some embodiments, the "inactive" layer and the electrode will be the same, i.e., the metal layer of the electrode functions as the inactive layer.

[0036] In some embodiments, the unimorph or bimorph actuators of the invention can be comprised of flexible (high compliance) materials, such as polymers, to provide high displacement at low actuation voltage. Examples of suitable polymer materials include - polyimide, kapton, and PVDF.

[0037] The unimorph, bimorph or multimorph actuator can be operated in one of two modes: (i) off-resonance mode and (ii) resonance mode. In the off-resonance mode, the displacement of the actuator can be controlled, via applied voltage from the ROIC, such that the actuator touches the bottom part of the sensor. A lower voltage approach can be adopted in the off-resonance mode by patterning a contact tip(s) on the uni- or bimorph actuator, such that the tip(s) can touch the bottom part of sensor. The tip reduces the displacement needed to thermally shunt the pixel, and can be driven by a smaller actuation voltage. The tip is small in width compared to the radiation wavelength, so that the cavity isn't significantly reduced in size.

[0038] Alternatively, the actuator can be operated in the resonance mode under a low voltage condition. A resonance approach offers lower voltage requirements and long battery life, with a controlled force exerted on the actuator tip without destroying the pixel. Keeping the actuator in resonance mode provides sufficient displacement to touch the pixel at lower voltages with enough integration time to cool the sensor. In resonance mode, the differential time with respect to background temperature is determined by the integrated time that the actuator is in contact with the pixel, and the pixel can attain its quiescent temperature between individual image frame rates (30 Hz or 60 Hz). In either mode (resonance or off- resonance) the voltage can be applied from the ROIC, or, if necessary, an off-ROIC source can be used.

[0039] When high compliance materials are used, the resonance frequencies can be lowered to provide higher displacements. The bottom part of the pixel can be touched with minimal force such that the pixel mechanical integrity will be preserved during the thermal shunting process. Various designs can be used to enhance the displacement with appropriate boundary conditions (varying the shape, size and the part of the actuator structure that needs to be anchored with the ROIC), without destroying the pixel architecture during the thermal shunting process.

[0040] For example, it may be desirable to increase the dimensions of the actuator such that the base of the actuator is positioned under one pixel, and the actuator is long enough to reach a distant pixel (for example 1, 2, 3, 4, 5 or more pixels away, by row or by column, in the array) when voltage is applied. In such a design, the actuators are straight and are staggered, so that each actuator touches a pixel distant from the pixel where the base of the actuator resides.

[0041] The ROIC 16 may be any suitable and/or desirable readout circuit suitable for processing the signals received from the sensor 12 and passing the processed signals to a device configured to further process the signal representative of the captured scene, such as a field-programmable gate array (FPGA). In some embodiments, the signal is further processed and displayed as an image on a screen. In other embodiments, the signal is further processed and used in other applications, for example a robotics application where it is important for locating an object in a scene, or a radiometric application, where it is important to determine the actual temperature of objects in a scene. Although only one sensor 12, one actuator 14, and one ROIC 16 are shown in Fig. 1, it will be appreciated that the imaging system 10 may include a plurality of sensors 12, for example a focal plane array, a plurality of actuators 14 and a plurality of pixel-level circuits in the ROIC 16. As will be understood by one skilled in the art, the focal plane array can comprise 160X120 pixels, 320X240 pixels, 640X480 pixels, or any other desired size, each pixel in the array being associated with (connected to) an actuator. Various embodiments of the system 10 are described in more detail herein below with respect to Figs. 2-5.

[0042] Figs. 2 and 3, which are each a cross section of the sensor 12 and ROIC 16, illustrate embodiments of the thermal imaging system 10 when the actuator 14 is in the first position (Fig. 2) and when the actuator 14 is in the second position (Fig. 3). As shown in Figs. 2 and 3, the sensor 12 includes a pixel 8 having first and second electrodes 18, 20 on opposite sides of thermally sensitive layer 19 (e.g., a thin-film pyroelectric layer), and the combination of support structures 24-1 and 24-2 and arms 22-1 and 22-2. Fig. 4 is a top view of the sensor 12 shown in Figs. 2 and 3.

[0043] The first electrode 18 may be considered as a "top" electrode of the sensor 12 and the second electrode 20 may be considered as a "bottom" electrode of the sensor 12. Desirably, the first electrode 18 is semi-transparent. In some embodiments, the first and second electrodes 18, 20 are both semi-transparent, and a reflective layer (not shown) is formed as the upper surface of actuator 14. In other embodiments, bottom electrode 20 is reflective. Both electrodes 18 and 20 may be fabricated from any suitable conductive material, and may form a portion of the electrical connection between sensor 12 and ROIC 16.

[0044] The system 10 further includes arms or leads 22-1 and 22-2 and posts 24-1 and 24-2 which also collectively form a portion of the electrical connection between the sensor 12 and the ROIC 16. More specifically, posts 24-1 and 24-2 extend vertically upward from contact pads 36-1 and 36-2 on ROIC 16 and tenninate adjacent diagonal comers 38-1 and 38-3 of pixel 8. Ami 22-1 (an elongated L-shaped ami) connects a top of post 24-1 to first electrode 18 adjacent corner 38-2 of pixel 8 (Fig. 4). Arm 22-2 (having an elongated L-shaped section 22-2-1 and a vertical section 22-2-2) connects a top of post 24-1 to second electrode 20 adjacent comer 38-4 of pixel 8 (Fig. 4) by way of a via or opening 40 formed in first electrode 18 and thermally sensitive layer 19 in or adjacent comer 38-4.

[0045] The amis 22-1 and 22 and posts 24-1 and 24-2 may be fabricated from any suitable conductive material. In addition to providing for an electrical connection between the sensor 12 and the ROIC 16, the arms 22-1 and 22and posts 24-1 and 24-2 also provide for thermal isolation between the sensor 12 and the ROIC 16. More specifically, the arms 22-1 and 22 and posts 24-1 and 24-2 are configured to support pixel 8 in spaced relation to ROIC 16via a gap 39. The gap 39 between pixel 8 and ROIC 16 can be formed by removal of one or more suitable sacrificial layers (not shown) that is/are utilized to initially hold pixel 8 and ROIC 16 in spaced relation prior to the formation of am s 22-1 and 22 and posts 24-1 and 24-2 that support pixel 8 in spaced relation to ROIC 16via a gap 39 after the removal of said one or more sacrificial layers.

[0046] Fig. 5 is a top view of an embodiment of the actuator 14. In this embodiment, the actuator 14 is shown as having a spiral-like or helical-like configuration, whereby variable gaps 26 exist between various portions of the actuator 14. Various portions of the actuator 14 are identified as portions 28, 30, 32 and 34 in Fig. 5, and it is apparent that, although not exactly to scale, Fig. 5 is drawn to indicate that the different portions 28, 30, 32, 34 may in some embodiments each have a different cross-section (e.g., a different width) associated therewith. In other embodiments, one or more of the different portions 28, 30, 32, 34 may have the same cross-section. When the actuator 14 is in the first position, the variable gaps 26 may be considered as fixed horizontal gaps. When the actuator 14 fully extends to the second position, the gaps may be considered to include both horizontal and vertical components. Due to the configuration of the actuator 14, when the actuator 14 is actuated, at least some of the different portions 28, 30, 32, 34 extend different distances from the ROIC 16 towards the sensor 12.

[0047] In a manner discussed hereinafter, actuator 14 can be formed on the top surface of ROIC 16 by any suitable and/or desirable semiconductor and/or MEM's processing technique(s). Regardless of how actuator 14 formed, the end of portion 28 of actuator 14 is affixed to the top surface of ROIC 16 while the remainder of actuator 14 is free to move as shown in Fig. 3. Desirably, ROIC 16 is also configured to apply suitable voltages to actuator 14.

[0048] As discussed above, actuator 14 is a piezoelectric actuator which can be of a unimorph configuration, a bimorph configuration, or a multimorph configuration. Regardless of configuration, at least one piezoelectric layer of each configuration receives a DC voltage, desirably from ROIC 16, which causes actuator 14 to move from the first position, with portion 34 of actuator 14 spaced from the pixel 8 (Fig. 2), to the second position with portion 34 of actuator 14 in contact with pixel 8, or vice versa, depending on the configuration of portion 34 of actuator 14 being either spaced from or in contact with pixel 8 when DC voltage is NOT applied. In this regard, the layers of materials forming actuator 14 can be configured whereupon actuator 14 is spaced from pixel 8 (Fig. 2) when DC voltage is NOT applied to actuator 14 and moves into contact with second electrode 20 of pixel 8 (Fig. 3) upon application of the DC voltage. Alternatively, the layers of materials forming actuator 14 can be configured to be in a stress state whereupon actuator 14 is in contact with second electrode 20 of pixel 8 (Fig. 3) when DC voltage is NOT applied and moves away from pixel 8 (Fig. 2) upon application of the DC voltage.

[0049] Other shapes of actuator 14 are also envisioned. In another embodiment, the spiral- shaped actuator 14 shown in Fig. 5 is replaced with a cantilever beam actuator 14-1, optionally with a small post 42 at the tip, that can touch the pixel 8, as shown in Figs. 6-8. In general, the actuator 14 can be designed to be of any size and shape (within the constraints provided by pixel size and the size of the gap 39 between the sensor and ROIC 16) so long as it can extend from the top surface of the ROIC 16 to the underside of the pixel 8 of the sensor 12 to provide thermal shunting, hi this regard, the layers of materials forming actuator 14-1 can be configured whereupon actuator 14-1 is spaced from pixel 8 when DC voltage is NOT applied to actuator 14-1 and the tip of actuator 14-1 (or the optional post 42) moves into contact with the bottom of pixel 8 upon application of the DC voltage. Alternatively, the layers of materials forming actuator 14 can be configured to be in a stress state whereupon the tip of actuator 14-1 (or the optional post 42) is in contact with the bottom of pixel 8 when DC voltage is NOT applied and the tip of actuator 14-1 (or the optional post 42) moves away from pixel 8 upon application of the DC voltage. In this embodiment, the gap 39 is small compared to the IR radiation wavelength to serve the purpose of the optical cavity.

[0050] In operation, the movement of actuator 14 or 14-1 permits detection of background radiance in the scene. In some embodiments, the movement of the actuator 14 or 14-1 will include touching of the actuator 14 or 14-1 to the bottom of pixel 8. h other embodiments, the movement of the actuator 14 or 14-1 will not include touching the bottom of pixel 8. The background radiance is subtracted from total radiance to provide a signal representing radiance of objects in a scene. The actuator 14 or 14-1 can operate as a self-chopper which enables the background radiation to be nulled out thermally, and provides a means to accurately calibrate pixel response for radiometric applications. Via ROIC 16 controlling a duty cycle of the actuator 14 or 14-1, an asymmetric chopping (or duty) cycle may be employed to significantly increase pixel response with no corresponding increase in noise. The asymmetric duty cycle may also be tailored to reduce response locally or globally to selectively increase dynamic range. Controlling the quiescent actuator voltage enables 2- color operation by adjusting the distance between the "top" reflective portion of the actuator 14 or 14-1 and the pixel element. When the actuator 14 or 14-1 is fully extended to come into contact with the pixel 8, the temperature of the pixel 8 will approach the temperature of the ROIC 16 within a few time constants. The temperature of ROIC 16 may be known, thereby providing a means to accurately calibrate pixel response to scene temperature.

[0051] In some embodiments, the actuator 14 or 14-1 may be fabricated by preparing a sacrificial layer on ROIC 16, depositing a layer (or layers) of inactive material or metal that result in strain when the piezoelectric layer is actuated, and depositing the piezoelectric layer and electrode materials at temperatures below about 400°C. In some embodiments, stress balancing approach between the layers may be followed by annealing or depositing various inactive thin film layers. For embodiments where the actuator 14 or 14-1 is configured to operate in the d33 mode (expansion along the axis of polarization), the upper electrode 18 will be interdigitated, with the interdigitated electrodes spaced closely enough to efficiently reflect long wave infrared radiation. Additionally, when the actuator 14 or 14-1 is not in the fully extended position, there is a sufficient distance between the first and/or second electrodes 18 and 20 and the actuator 14 or 14-1 to minimize capacitive coupling from the actuator 14 or 14-1 to the pixel element.

Γ00521 Example

[0053] A piezoelectric thin film actuator 14 or 14-1 will be integrated underneath a pixel 8 in the manner described below. It is to be appreciated however, that a plurality of thin film actuators 14 or 14-1 can be integrated underneath a plurality of pixels 8 in the same manner.

[0054] 1. A ROIC 16 will be coated with a sacrificial layer such as polyimide following a standard spin-on technique.

[0055] 2. Vias will be etched into the sacrificial layer following standard reactive-ion etching (RIE) technique. Thin film metal will be deposited, patterned and etched onto the patterned, sacrificial layer for d31 actuator operation. The bottom metal layer makes contact with the ROIC either for the electrical signal or a ground connection to ROIC 16.

[0056] 3. A piezoelectric layer such as A1N, ZnO or PZT will be grown directly using sputtering onto the metallized/sacrificial layer below about 450° C to prevent damage to ROIC 16.

[0057] 4. The piezoelectric layer will be patterned in conjunction with the bottom metal electrode, determining the final shape of the actuator 14 or 14-1.

[0058] 5. A continuous metallic layer will be deposited onto the piezoelectric layer using sputtering followed by patterning using lithographic technique. The top electrode will make contact with the ROIC 16 by way of a via for a d31 unimorph actuator.

[0059] 6. Once arrays of actuators 14 or 14-1 are fabricated, 1 to 2 microns thick parylene-C will be deposited. Then, wafer bonding will be employed to attach an electroded pyroelectric film.

[0060] 7. After pixels 8 are built, the pixels 8 and actuators 14 or 14-1 will be released using oxygen plasma etching/ashing technique.

[0061] Although the invention has been described in terms of particular embodiments in this application, one of ordinary skill in the art, in light of the teachings herein, can generate additional embodiments and modifications without departing from the spirit of, or exceeding the scope of, the described invention. Accordingly, it is understood that the drawings and the descriptions herein are proffered only to facilitate comprehension of the invention and should not be construed to limit the scope thereof.

Claims

The Invention Claimed Is:

1. A thermal imaging system comprising:

a thermal sensor;

a readout circuit in spaced relation to the thermal sensor; and a piezoelectric actuator coupled to the readout circuit and under the control of the readout circuit for causing a portion of the piezoelectric actuator to move from a first state spaced from the thermal sensor to a second state either in contact with the thermal sensor or in closer proximity to the thermal sensor than the first state and vice versa.

2. The thermal imaging system of claim 1, wherein the portion of the piezoelectric actuator includes a tip.

3. The thermal imaging system of claim 1, wherein the readout circuit applying a voltage to the piezoelectric actuator causes the piezoelectric actuator to move from the first state to the second state or vice versa.

4. The thermal imaging system of claim 1, wherein the thermal sensor comprises at least one pixel, and each pixel includes electrical interconnects that connect the pixel to the readout circuit and which maintain the readout circuit in spaced relation to the pixel.

5. The thermal imaging system of claim 4, wherein the pixel elements are formed from pyroelectric material.

6. The thermal imaging system of claim 1, wherein the piezoelectric actuator is one of the following: a unimorph actuator, a bimorph actuator, or a multimorph actuator.

7. The thermal imaging system of claim 1, wherein the piezoelectric actuator has one of the following configurations: a d31 configuration or a d33 configuration.

8. The thermal imaging system of claim 1, wherein the system comprises a plurality of thermal sensors and a plurality of piezoelectric actuators.

9. The thermal imaging system of claim 8, wherein the plurality of themial sensors and a plurality of piezoelectric actuators comprise a 160X120, a 320X240, or 640X480 focal plane array.

10. The thermal imaging system of claim 1, wherein the piezoelectric actuator is spiral shaped or in the shape of a beam.

11. A method of detecting radiance of objects in a scene, comprising: a) providing a thermal imaging system comprising a piezoelectric actuator disposed between a themial sensor and a readout circuit;

b) detecting total radiance in the scene with the themial sensor; c) detecting background radiance in the scene by movement of at least a portion of the piezoelectric actuator between the themial sensor and the readout circuit; and

d) subtracting the background radiance detected in step (c) from total radiance detected in step (b) to provide a signal representing radiance of objects in a scene.

12. The method of claim 11, wherein the movement of the actuator includes touching the sensor.

13. The method of claim 11 , wherein the movement of the actuator does not include touching the sensor.

14. The method of claim 11, wherein the actuator operates in resonance mode.

15. The method of claim 11, wherein the actuator operates in off- resonance mode.

16. The method of claim 11 , wherein the actuator includes a duty cycle.

17. The method of claim 11, further including moving the piezoelectric actuator in contact with the thermal sensor and the readout circuit.