Roland W. Gooch

A vacuum packaged surface micromachined resonant accelerometer

This paper describes the operation of a vacuum packaged resonant accelerometer subjected to static and dynamic acceleration testing. The device response is in broad agreement with a new analytical model of its behavior under an applied time-varying acceleration. Measurements include tests of the scale factor of the sensor and the dependence of the output sideband power and the noise floor of the double-ended tuning fork oscillators as a function of the applied acceleration frequency. The resolution of resonant accelerometers is shown to degrade 20 dB/decade beyond a certain characteristic acceleration corner frequency. A prototype device was fabricated at Sandia National Laboratories and exhibits a noise floor of 40 /spl mu/g//spl radic/(Hz) for an input acceleration frequency of 300 Hz.

Amorphous Silicon Microbolometer Technology

Highly sensitive hydrogenated amorphous silicon (a-Si:H) microbolometer arrays have been developed that take advantage of the high temperature coefficient of resistance (TCR) of aSi:H and its relatively high optical absorption coefficient. TCR is an important design parameter and depends on material properties such as doping concentration. Ultra-thin (∼2000 A) aSiN x :H/a-Si:H/ a-SiN x :H membranes with low thermal mass suspended over silicon readout integrated circuits are built using RF plasma enhanced chemical vapor deposition (PECVD) and surface micromachining techniques. The IR absorptance of the bolometer detectors is enhanced by using quarter-wave resonant cavity structures and thin-film metal absorber layers. To ensure high thermal isolation the microbolometer arrays are vacuum packaged using wafer level vacuum packaging. Imaging applications include a 120×160 a-Si:H bolometer pixel array IR camera operating at ambient temperature. Non-imaging applications are multi-channel detectors for gas sensing systems.

Low-cost low-power uncooled a-Si-based micro infrared camera for unattended ground sensor applications

Low power and low cost are primary requirements for an imaging infrared camera used in unattended ground sensor arrays. In this paper, an amorphous silicon (a-Si) microbolometer-based uncooled infrared camera technology offering a low cost, low power solution to infrared surveillance for UGS applications is presented. A 15 X 31 micro infrared camera (MIRC) has been demonstrated which exhibits an f/1 noise equivalent temperature difference sensitivity approximately 67 mK. This sensitivity has been achieved without the use of a thermoelectric cooler for array temperature stabilization thereby significantly reducing the power requirements. The chopperless camera is capable of operating from snapshot mode (1 Hz) to video frame rate (30 Hz). Power consumption of 0.4 W without display, and 0.75 W with display, respectively, has been demonstrated at 30 Hz operation. The 15 X 31 camera demonstrated exhibits a 35 mm camera form factor employing a low cost f/1 singlet optic and LED display, as well as low cost vacuum packaging. A larger 120 X 160 version of the MIRC is also in development and will be discussed. The 120 X 160 MIRC exhibits a substantially smaller form factor and incorporates all the low cost, low power features demonstrated in the 15 X 31 MIRC prototype. In this paper, a-Si microbolometer technology for the MIRC will be presented. Also, the key features and performance parameters of the MIRC are presented.

Low-cost low-power uncooled 120x160 a-Si-based microinfrared camera for law enforcement applications

Low power and low cost are primary requirements for an imaging infrared camera serving law enforcement applications. These include handheld, vehicle and helmet mounted systems for search and surveillance applications. In this paper, a 120 X 160 amorphous silicon (a-Si) microbolometer-based uncooled infrared camera technology offering a low cost, low power solution to infrared surveillance for UGS applications is presented. A 120 X 160 micro infrared camera has been demonstrated which exhibits a noise equivalent temperature difference sensitivity approximately 50 mK using f/1 optics and approximately 80 mK using f/1.2 optics. This sensitivity has been achieved without the use of a thermoelectric cooler for array temperature stabilization thereby significantly reducing the power requirements.

Low-cost low-power uncooled a-Si-based micro infrared camera

An amorphous silicon (a-Si) microbolometer-based uncooled infrared camera technology, offering a low- cost, low-power solution to infrared surveillance for both civilian and military application is presented. A- Si exhibits a temperature dependent resistance with a 3000K temperature coefficient of resistance (TCR) of 2.7 percent/K. The uncooled a-Si microbolometer detector structure employs a low thermal mass a-Si membrane structure with high thermal isolation legs monolithically integrated on a CMOS readout integrated circuit (ROIC) chip. A refractive resonant cavity design results in approximately 90 percent infrared absorptance over the 8-13 um spectral band. A-Si also exhibits a UV/visible photoconductive response for multispectral applications. The ROIC involves an integrating amplifier per pixel and a column multiplexed output. A 15 x 31 micro infrared camera (MIRC) has been developed, which exhibits f/l noise equivalent temperature difference, thereby significantly reducing the power requirements. The 15 x 31 camera demonstrated exhibits a 35 mm camera form factor employing a low cost f/l singlet optic and LED display, as well as low cost vacuum packaging. A larger 120 x 160 version of the MIRC is also in development and will be discussed.

New fabrication techniques for high dynamic range tunneling sensors

We have developed high dynamic range (105-106 gs) tunneling accelerometers1,2 that may be ideal for smart munitions applications by employing both surface and bulk micromachining processing techniques. The highly miniaturized surface-micromachined devices can be manufactured at very low cost and integrated on chip with the control electronics. Bulk-micromachined devices with Si as the cantilever material should have reduced long-term bias drift as well as better stability at higher temperatures. Fully integrated sensors may provide advantages in minimizing microphonics for high-g applications. Previously, we described initial test results using electrostatic forces generated by a self-test electrode located under a Au cantilever3. In this paper, we describe more recent testing of Ni and Au cantilever devices on a shaker table using a novel, low input voltage (5 V) servo controller on both printed wiring board and surface-mount control circuitry. In addition, we report our initial test results for devices packaged using a low-temperature wafer-level vacuum packaging technique for low-cost manufacturing.

Advances in small-pixel, large-format α-Si bolometer arrays

Continued reduction of α-Si bolometer pixel size has led to increases in array size as well as improvements in temporal response for a given level of sensitivity. Programs funded by DARPA and NVESD are developing advanced 320×240, 640×480 and 1024×768 α-Si bolometer arrays with 17μm pixels, on-chip A/D conversion, significant improvements in dynamic range, significant reductions in thermal time constant and other specialized functions. The push to 17μm is motivated not only by system size and weight, but also by improvements in performance resulting from increased resolution. Smaller pixels permit fabrication of larger arrays without subverting the field-size constraints of ordinary photolithographic processes. Reducing pixel size also reduces the effects of stress mismatches. This permits reduction of device thickness, thereby reducing thermal time constant. Improvements in bolometer material properties have served to improve responsivity while lowering 1/f noise. Because these arrays substantially reduce sensor size, they are becoming the preferred format for most applications, particularly for weapon sights and for head-mounted and UAV applications. The larger array sizes are of interest for pilotage and surveillance.

a-Si 160 x 120 micro IR camera: operational performance

Amorphous silicon (a-Si) microbolometer technology is a silicon fab-compatible uncooled detector technology which offers a low cost, high volume approach for infrared sensor and imager applications. Raytheon has used this detector technology to develop a 160x120 a-Si based infrared camera. The systems goal was to develop an affordable infrared imaging product that provides acceptable performance for many commercial and military applications. To meet low power goals, a non-temperature controlled detector approach was required. This led to the challenge of developing a technique for operating over ambient temperature that includes correction techniques that account for offset and responsivity non-uniformities over ambient operating temperature. This paper describes the operating performance parameters of a typical a-Si 160 X 120 IR camera. This camera is currently entering production, and will be produced by the Raytheon Commercial Infrared business.

Low-power uncooled 120x160 a-Si-based micro infrared camera for unattended ground sensor applications

Low power and low cost are primary requirements for an imaging infrared camera used in unattended ground sensor arrays. In this paper, a 120 X 160 amorphous silicon (a- Si) microbolometer-based uncooled infrared camera technology offering a low cost, low power solution to infrared surveillance for UGS applications is presented. A 120 X 160 micron infrared camera (MIRC) has been demonstrated which exhibits an f/1 noise equivalent temperature difference sensitivity approximately 63 mK. This sensitivity has been achieved without the use of a thermoelectric cooler for array temperature stabilization thereby significantly reducing the power requirements. Chopperless camera operation at a 20 Hz frame rate with power consumption of 380 mW has also been demonstrated. The 120 X 160 MIRC operates under digital signal processor (DSP) control. To reduce cost, this DSP-controlled architecture employs commercial off-the-shelf DSP, A/D, memory and voltage regulator chips. The detector chip, employing an integrating amplifier per unit cell ROIC design, is the single custom chip used. The camera also employs low cost f/1 optics, as well as low cost wafer-level vacuum packaging. In this paper, a-Si microbolometer technology for the MIRC will be presented. Also, the key features and performance parameters of the MIRC are presented.