Nickel oxide (NiO) film was formed on the SiO<sub>2</sub>/Si substrate at the room temperature with water cooling system by
reactive RF sputter. The feasibility of bolometric material was investigated, and a microbolometer using the NiO film
was fabricated and evaluated. The NiO films were analyzed by using grazing-incidence X-ray diffraction (GIXRD). The
NiO(111), NiO (200), and NiO (220) peaks expected as the main spectrum were dominantly appeared on the
polycrystalline NiO films. The representative resistivity acquired at the O<sub>2</sub>/(Ar+O<sub>2</sub>) ratio of 10% sample was about
40.6 Ωcm. The resistivity of 40.6 Ωcm obtained in low oxygen partial pressure was inclined to reduce to 18.65 Ωcm
according to the increase of the O<sub>2</sub>/(Ar+O<sub>2</sub>) ratio. The TCR value of fabricated microbolometer was −1.67%/℃ at the
NiO film resistivity of 40.6 Ωcm. The characteristics of fabricated NiO film and microbolometer were demonstrated by
XRD patterns, TCR value, and SEM image.
In this report, we describe thin 200nm thick GaN film formation technology on Si which allows microbolometer
application. GaN layer with AlN buffer layer obtained by the MOCVD has TCR of about -0.64 %/°C and sheet
resistance of ~2800 ohm/sq. Acquired GaN films were analyzed by XRD, SEM, Hall measurement, and etc. The
successful growth of thin single crystalline or polycrystalline GaN film on Si can be a good semiconductor bolometric
material. And the multi wavelength detecting systems with GaN based devices including UV detector, power devices,
amplifier with GaN and AlGaN MOSFET, HEMT, and etc can be realized. We obtained thin(~200nm) crystalline GaN
layer on Si(111) with AlN buffer layers with FWHM(full width at half maximum) of ~1800 arcsec. And its bolometric
characteristic was analyzed.
In this report, we describe the two different nickel oxide film formation processes for microbolometer application:
the heat treatment of nickel metal and the reactive sputtering. Nickel oxide films obtained by the heat treatment of nickel
show high TCR(about -3.2/°C) and low 1/f noise characteristic. The reactively sputtered nickel oxide films have the wide
range of resistivity according to the sputtering vacuum level, time, and O<sub>2</sub>/Ar gas partial pressure. The acquired TCR of
sputtered films are in the range of -1.4%/°C and -3.45%°C. And the 1/f noise parameter k, which shows the performance
between VOx and a-Si, is as low as 8.5×10<sup>-13</sup> at the TCR of -1.75%/°C. Acquired nickel oxide films were analyzed from
XRD, AFM methods, and etc. It is regarded that the resistivity variation of polycrystalline nickel oxide film comes from
nonstoichiometric property of nickel and oxygen atoms. We simulated the optic and membrane structure for predicting
the performance of a microbolometer with nickel oxide film. The estimated NETD(noise equivalent temperature
difference) for the 50μmx50μm size of pixel is NETD below 20mK.
A radiation-resistant readout integrated circuit for focal plane arrays was studied to improve the reliability of infrared
image systems operating in a radioactive environment, such as in space or in the surroundings of a nuclear reactor. First,
as radiation-hardened NMOSFET structure, which includes a layout modification technique, was proposed. The readout
integrated circuit for infrared focal plane arrays was then designed on basis of the proposed NMOSFET layout.
Commercial 0.35 um process technology was used to fabricate the proposed unit NMOSFET and the designed readout
integrated circuit which is based on the proposed NMOSFET. The measured electrical characteristics of the fabricated
unit NMOSFET and readout integrated circuit are in good agreement with the simulated results. For verification of the
radiation tolerance, the fabricated chip was exposed to 1 Mrad (Si) of gamma radiation, which is high enough to
guarantee reliable usage in space or in a very harsh radiation environment. While exposed to gamma radiation, the
fabricated chip was connected to a power supply (3.3 V) for testing under the worst conditions. After being exposed to
1 Mrad of gamma radiation, the unit NMOSFET showed only a slight increment of a few picoamperes in the leakage
current, and the designed readout integrated circuit showed little change at an output voltage of less than 10% of a proper
output voltage. The changes in the characteristics of the unit NMOSFET and the designed readout infrared integrated
circuit are at an allowable level in relation to process variation.
This study investigates the feasibility of a reactively sputtered thin nickel oxide film for application to a
microbolometer. The properties of the developed thin nickel oxide film depend on the sputter process parameters. The
measured resistivity of the nickel oxide films ranges from 0.3 Ωcm to approximately 50 Ωcm. Negative Temperature
Coefficient of Resistance (TCR) values as high as -3.3%/ °C were acquired. The feasible 1/f noise characteristic was also
measured. The magnification of the TCR value and 1/f noise of the nickel oxide films was proportional to the resistivity
of the nickel oxide films. Specifically, nickel oxide film with a high resistivity showed a higher TCR value and more 1/f
noise. From the measured TCR and 1/f noise values, the theoretically calculated NETD showed a value suitable for use
with a microbolometer. Additionally, an analysis of sputtered thin nickel oxide films was conducted through X-ray
This study represents an investigation of the feasibility of thin nickel oxide film (~100nm in thickness) as a microbolometer
material. Thin nickel oxide film was obtained by a heat treatment (below 400 °C) of DC-sputtered Ni film on a
SiO2/Si substrate in an O2 environment.
Using a parameter analyzer (4156A) with a TEC temperature controller, a spectrum analyzer and a low noise
amplifier, a systemic analysis of the electrical and noise characteristics of nickel oxide film is performed.
A negative temperature coefficient of resistance (TCR) value of 3.28%/oC and a feasible 1/f noise result ranging from
1Hz to 100Hz were acquired. The characteristics of the thin nickel oxide film obtained in this study are comparable to
those of a-Si. Moreover, the nickel oxide thin film retained a stable state at room temperature.
Thus, the thin nickel oxide, which is CMOS-compatible and yields high TCR values and proper 1/f noise
characteristics through a simple fabrication process, is shown to be a promising micro-bolometric material.
The function of most readout integrated circuits (ROIC) for microbolometer focal plane arrays (FPAs) is supplying a
bias voltage to a microbolometer of each pixel, integrating the current of a microbolometer, and transferring the signals
from pixels to the output of a chip. However, the scale down of CMOS technology allows the integration of other
functions. In this paper, we proposed a CMOS ROIC involving a pixel-level analog-to-digital converter (ADC) for 320
× 240 microbolometer FPAs. Such integration would improve the performance of a ROIC at the reduced system cost
and power consumption. The noise performance of a microbolometer is improved by using the pixelwise readout
structure because integration time can be increased up to 1ms.
A Pixel circuit is consisted of a background skimming circuit, a differential amplifier, an integration capacitor and a 10-bit DRAM. First, the microbolometer current is integrated for 1ms after the skimming current correction. The
differential amplifier operates as an op-Amp and the integration capacitor makes negative feedback loop between an
output and a negative input of the op-Amp. And then, the integrated signal voltage is converted to digital signals using a
modified single slope ADC in a pixel when the differential amplifier operates as a comparator and the 10-bit DRAM
stores values of a counter. This readout circuit is designed and fabricated using a standard 0.35μm 2-poly 3-metal
An uncooled capacitive type bimaterial infrared detector with high fill-factor and improved noise characteristic is
investigated. Top electrode is insulated from the substrate thermally as well as electrically. Only small dimension
(10μmx2μmx0.2μm) of SiO<sub>2</sub> only layer (thermal insulation leg) assures thermal conductance of 1.06x10<sup>-7</sup>W/K, while keeping the infrared absorber (top electrode) separated from the bias signal. Due to the decreased thermal isolation leg length, high fill-factor of 0.77 is achieved. The bimaterial leg that connects the infrared absorber to the thermal insulation leg is a 38μm long cantilever structure composed of Al and SiO<sub>2</sub> bi-layer, which has large difference in the thermal expansion coefficient (Al:25ppm/K and SiO2:0.35ppm/K). Bimaterial leg length (38μm) is quite shorter than the
previously designed device, resulting in the decreased bending of the bimaterial leg. However, the increased fill-factor
reduces temperature fluctuation noise term that is inversely proportional to the absorber area, and it is found by FEM
simulation that the enhanced mechanical properties such as spring constant reduce the thermo-mechanical noise term of
the proposed device.
Pixelwise integrated circuits involving a pixel-level analog-to-digital converter (ADC) are studied for 320 × 240
microbolometer focal plane arrays (FPAs). It is necessary to use the pixelwise readout architecture for decreasing the
thermal noise. However, it is hard to locate a sufficiently large integration capacitor in a unit pixel of FPAs because of
the area limitation. To effectively overcome this problem, a two step integration method is proposed.
First, after integrating the current of the microbolometer for 32&mgr;s, upper 5bits of the 13bit digital signal are output
through a pixel-level ADC. Then, the current of the microbolometer is integrated during 1ms after the skimming current
correction using upper 5bits in a field-programmable gate array (FPGA), and then lower 8bits are obtained through a
pixel-level ADC. Finally, upper 5bits and lower 8bits are combined into the digital image signal after the gain and offset
correction in digital signal processor (DSP)
Each 2×2 pixel shares an readout circuit, including a current-mode background skimming circuit, an operational
amplifier(op-Amp), an integration capacitor and a single slope ADC. When the current of a microbolometer is
integrated, the integration capacitor is connected between a negative input and an output of the op-Amp. Therefore a
capacitive transimpedance amplifier (CTIA) has been employed as the input circuit of the microbolometer. When the
output of a microbolometer is converted to digital signal, the Op-Amp is used as a comparator of the single slope ADC.
This readout circuit is designed to achieve 35×35&mgr;m<sup>2</sup> pixel size in 0.35&mgr;m 2-poly 3-metal CMOS technology.
In this paper, a novel high SNR readout circuit for a satellite TDI array is presented. Since an input range of an IR image for environmental satellites is broad and especially the cloud top temperature (CTT) that is important in understanding phenomena of atmosphere is quite low, the readout of low temperature signal is important in satellite applications. However, the noise resulted from a readout circuit is no longer ignorable compared to a detector shot noise at low IR radiation. Hence, an adaptive charge capacity control method is proposed in this paper for an improved SNR at low temperature. It is found that SNR is improved as much as 11dB at 200K and 90% background-limited infrared photodetection (BLIP) condition is satisfied over a total input range by simulation.
By adopting new capacitance reading scheme, a capacitive type uncooled infrared detector structure with high fill-factor
and effectively controllable thermal conductance is proposed. Instead of conventional MEMS capacitor structure (i.e. an
insulating gap between top and bottom electrodes), a capacitor with a floating electrode and two bottom electrodes has
been applied to the infrared detector. Infrared absorber which also acts as the floating electrode of the capacitor is
connected to the substrate via two bimaterial legs. These legs consist of two materials having large difference in thermal
expansion coefficient (Al: 25ppm/K and SiO<sub>2</sub>: 0.35ppm/K), so that the legs are deflected according to the certain
temperature change due to the infrared absorption. This leg's movement results in the displacement of the top electrode
of the capacitor, and infrared is sensed by measuring the capacitance change. However, the one end tip of the bimaterial
leg does not contain Al and consist of SiO<sub>2</sub>, solely. This leg design enables the absorber to be separated from the
substrate thermally as well as electrically, because insulators usually have low thermal conductivity than metals more
than an order. The capacitance change by the result of infrared absorption is read only through two bottom electrodes
which are placed right under the absorber, and also perform as infrared reflectors. The design has advantages of
enlarging fill-factor of the infrared detector, effective thermal conductance controlling and high sensitivity to IR. With
only small dimensions of SiO<sub>2</sub> (10μm x 2μm x 0.2μm), the device can have low thermal conductance of 1.3x10<sup>-7</sup>W/K,
so that the portion of the legs can be reduced in a pixel area. The device has fill-factor of 0.77 and 14%/K of sensitivity
to infrared rays concerning 1~2K of temperature difference between the structure and the substrate.
At present, infrared photodetectors are being increasingly used in space systems, where they are exposed to the space radiation environment. Consequently, the radiation-hardness-related problem in HgCdTe photodetectors has become a critical issue.
In this study, the gamma radiation effects on ZnS- and CdTe-passivated mid-wavelength infrared (MWIR) HgCdTe photodiodes were investigated. Although ZnS has an excellent insulating property, its radiation-tolerant property was revealed very poor in comparison with CdTe. After 1 Mrad of gamma irradiation, the resistance-area product at zero bias (R<sub>0</sub>A) value of the ZnS-passivated photodiode was drastically reduced by roughly 5 orders from ~10<sup>7</sup> Ω cm<sup>2</sup> to 10<sup>2</sup> Ω cm<sup>2</sup>, whereas the CdTe-passivated photodiode showed no degradation in R<sub>0</sub>A values.
In this paper, a readout circuit (ROIC) utilizing a novel noise tolerant edge detection technique for InSb medium wavelength infrared focal plane arrays (MWIR FPAs) is studied. The use of a noise tolerant edge detection algorithm eliminates the need for a pixel-level non-uniformity correction circuit. In addition, the proposed circuit's simple structure allows the processing circuits to be integrated within a shared 2 by 2 pixel area. The proposed method shows better performance for the Gaussian and salt & pepper noise than other conventional approaches. A good edge map is obtained in general InSb MWIR detectors which have 99.5% operability and about 5% non-uniformity of the pixel current. Basic operation of the fabricated noise tolerant edge detection circuit is demonstrated.
We have developed a microbolometer readout integrated circuit (ROIC) that corrects the non-uniformity in analog operation and acts in both normal mode and edge detection mode. A capacitive transimpedance amplifier (CTIA) has been employed as the input circuit of the microbolometer. Generally, when fabricating microbolometer focal plane arrays (FPAs), offset-error and gain-error in the inter-microbolometer are induced by fabrication error. They are shown as fixed pattern noise (FPN) in the infrared image. In the present study, a circuit correcting the offset-error and the gain-error in the normal mode by controlling the bias and the integration capacitance of the CTIA is proposed. This circuit does not require an additional DSP chip, and the non-uniformity is corrected before the analog to digital conversion (ADC). Thus, it can utilize 3-4 bits lower ADC compared to the conventional readout circuit. In the edge detection mode, after correcting the gain-error in two adjacent pixels, edge detection can be realized by subtracting their signal without the DSP. We have designed the suggested circuit to output a 10bit level effective infrared signal using 0.35um 2-poly 3-metal CMOS technology.
We are performing a research on the application of an adaptive optics system to upgrade the beam quality of a laser. We consider the adaptive optics system to consist of a bimorph mirror, a Shack-Hartmann sensor and a control system. Since the laser beam can be circular, annulus or square/rectangle, we predicted the performance of a circular bimorph deformable for each different beam shapes. We selected a bimorph mirror of 120 mm clear aperture with 31 actuators as a design candidate. Firstly we found that the fitting ability of the bimorph mirror for a circular/annulus beam can significantly improve by limiting the correctable area to an annulus of 100mm outer diameter and 20mm inner diameter, which our square laser beam fits into. This study shows that the bimorph mirror, which might be considered as a modal controller, can compensate the square lower order aberrations with fitting abilities larger than 0.95 for tilt, defocus, coma and astigmatism, and 0.82 for spherical aberration. Finally we concluded that the circular bimorph mirror is perfectly okay for square laser beam compensating.
The capacitance-voltage (C-V) and the Hall effect measurements were used, in order to study electron cyclotron resonance (ECR) plasma damage in HgCdTe (MCT). In this study using ECR treatments of MCT and C-V measurements, we observed that the type conversion of MCT surface largely depended on the ECR etching conditions, when MCT was etched by ECR plasma as a function of the ECR power and dc bias. The n-type conversion was not observed when the p-type MCT was etched under the condition of ECR power 150 W and dc bias -20 V. As dc bias of ECR increased over -40 V at the constant ECR power 150 W, the p-type MCT was converted to n-type. The p-type MCT was also converted to n-type when ECR power increased to 500 W at the constant dc bias -20 V. These results probably were due to the inter-diffusion of a large amount of excess mercury, liberated during the ECR treatment, into MCT, which were similar to the results of ion milling process. Another interesting result, observed in C-V measurements, was the p- type conversion from n-type MCT when the n-type MCT was etched under the condition of ECR power 150 W and dc bias -20 V. As dc bias of ECR increased over -40 V, the C-V curve was the results of n-type MCT characteristics. We considered that a low dc bias of -20 V, the hydrogen passivation and the deficiency of mercury in the etched surface were dominant and resulted in conversion to p-type. As dc bias increased over -40 V, the inter-diffusion of excess mercury into MCT was dominant and associated with keeping the n-type characteristics.
The surface of mercury cadmium telluride (Hg<SUB>1-x</SUB>cd<SUB>x</SUB>Te, x approximately equals 0.2) was etched by electron cyclotron resonance (ECR) plasma utilizing a mixture of CH<SUB>4</SUB> and H<SUB>2</SUB>. The etch rate was optimized as a function of mix ratio of H<SUB>2</SUB>/CH<SUB>4</SUB> ECR power, total pressure, and DC bias voltage in order to arrive at smooth surface. The etched surface of HgCdTe was characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), FT-IR and Hall effect measurements. Optimized etching conditions were 25% CH<SUB>4</SUB>, ECR power of 200 watts, total pressure of 5-7 mtorr and bias voltage of -80 V. XPS analysis revealed that atomic concentration of Hg and Te decreased, but that of Cd increased, indicating preferential etching. Also, hall effect measurement indicated increased carrier density, but decreased mobility of HgCdTe.
Proc. SPIE. 2513, 21st International Congress on: High-Speed Photography and Photonics
KEYWORDS: Signal to noise ratio, Digital signal processing, Digital image processing, Sensors, Image processing, Digital filtering, Signal processing, Analog electronics, Electronic filtering, Signal detection
This paper describes the digital image processing techniques of a thermal observation system, which is a serial/parallel scan and standard TV display type using a SPRITE (Signal PRocessing In The Element) detector. The designed digital electronics has two major signal processing stages: a high speed digital scan converter and an autoregressive (AR) filter. The digital scan converter is designed with analog-to-digital converter (ADC) and dual port RAM that can carry out reading and writing simultaneously, thus enabling compact scan conversion. The scan converter reformats the five parallel analog signals generated from the detector elements into serial digital signals compatible with RS-170 video rate. For the improvement of signal-to- noise ratio and compensation for the gamma effect of the monitor, we have implemented a real time 1st order AR filter that adopts frame averaging method. With the look-up-table (LUT) ROM that contains the frame averaging factors and the gamma coefficients, this digital filter performs the noise reduction and the gamma correction at the same time. This digital image processor has been proven to provide excellent image quality and superior detection capability for distant targets at night time.