Uncooled Infrared Image Sensor Research Articles

Averaging Pixel Current Adjustment Technique for Reducing Fixed Pattern Noise in the Bolometer-Type Uncooled Infrared Image Sensor.

In this paper, we propose an averaging pixel current adjustment technique for reducing fixed pattern noise (FPN) in the bolometer-type uncooled infrared image sensor. The averaging pixel current adjustment technique is composed of active pixel, reference pixel, and calibration circuit. Polysilicon resistors were used in each active pixel and reference pixel. Resistance deviation among active pixels integrated with the same resistance value cause FPN. The principle of the averaging pixel current adjustment technique for removing FPN is based on the subtraction of dark current of the active pixel from the dark current of the reference pixel. The subtracted current is converted into the voltage, which contains pixel calibration information. The calibration circuit is used to adjust the calibration current. After calibration, the nano-ampere current is output with small deviation. The proposed averaging pixel current adjustment technique is implemented by a chip composed of a pixel array, a calibration circuit, average current generators, and readout circuits. The chip was fabricated using a standard 0.35 μm CMOS process and its performance was evaluated.

An Analog-Front ROIC with On-Chip Non-Uniformity Compensation for Diode-Based Infrared Image Sensors.

This paper proposes a CMOS front-end readout-integrated circuit (ROIC) with on-chip non-uniformity compensation technique for a diode-based uncooled infrared image sensor. Two techniques are adopted to achieve on-chip non-uniformity compensation: a reference dummy metal line is introduced to alleviate the dominant non-uniformity with IR-drop presented in large pixel array, and a current splitting architecture-based variable current source for diode bias is proposed to compensate other residual non-uniformity. A differential integrator is chosen as the main amplifier of readout circuit for its superior noise performance. For low power design, a pulse-powered row buffer is designed in this work. The proposed ROIC for 384 × 288 diode-based detector array is fabricated with a 0.35-m CMOS process. It occupies an area of 4.4 mm × 15 mm, and the power consumption is 180 mW. The measured result shows that with the proposed on-chip non-uniformity compensation, the output voltage variation is greatly reduced from 2.5 V to 60 mV.

Absorption Properties of Simply Fabricated All-Metal Mushroom Plasmonic Metamaterials Incorporating Tube-Shaped Posts for Multi-Color Uncooled Infrared Image Sensor Applications

Wavelength-selective infrared (IR) absorbers have attracted considerable interest due to their potential for a wide range of applications. In particular, they can be employed as advanced uncooled IR sensors that identify objects through their radiation spectra. Herein, we propose a mushroom plasmonic metamaterial absorber incorporating tube-shaped metal posts (MPMAT) for use in the long-wavelength IR (LWIR) region. The MPMAT design consists of a periodic array of thin metal micropatches connected to a thin metal plate via tube-shaped metal posts. Both the micropatches and posts can be constructed simultaneously as a result of the tube-shaped structure of the metal post structure; thus, the fabrication procedure is both simple and low cost. The absorption properties of these MPMATs were assessed both theoretically and experimentally, and the results of both investigations demonstrated that these devices exhibit suitable levels of LWIR absorption regardless of the specific tube-shaped structures employed. It was also found to be possible to tune the absorption wavelength by varying the micropatch width and the inner diameter of the tube-shaped metal posts, and to obtain absorbance values of over 90%. Focal plane array structures based on such MPMATs could potentially serve as high-performance, low-cost, multi-spectral uncooled IR image sensors.

Systematic Investigation on Deposition Temperature Effect of Ni1–xO Thin Films for Uncooled Infrared Image Sensor Applications

Nickel oxide (Ni1– x O) films deposited by RF reactive magnetron sputtering were investigated at various substrate temperatures ranging from room temperature to 250 °C for uncooled infrared image sensor applications. The structural properties measured by X-ray diffraction and X-ray photoelectron spectroscopy showed that the deposited films had a Ni-deficient structure and that films deposited at a higher temperature showed more crystallized structures with fewer microstructural defects. These defects had an effect on several properties influencing the sensing performance. The conductivity was found to decrease from 9.47 to 0.10 S/cm with the deposition temperature. In addition, with an increase in the deposition temperature, both the absolute temperature coefficient of resistance and the normalized Hooge parameter, representing the magnitude of 1/ $f$ noise, increased from 1.56%/K to 2.76%/K and from $9.12\times 10^{\mathrm {-28}}$ to $2.40\times 10^{\mathrm {-27}}~\text{m}^{\mathrm {3}}$ , respectively. ( $\alpha _{{H}}$ /n) $^{\mathrm {1/2}}/\vert \beta \vert $ , a useful figure of merit determining the performance of infrared sensor, was varied in the range of $1.77\times 10^{\mathrm {-14}}$ and $2.06\times 10^{\mathrm {-14}}~\text{m}^{\mathrm {3/2}}\text{K}$ /% with the deposition temperature, and the best performance was obtained from the film deposited at 250 °C. Consequently, the nickel oxide film is deemed to be a good potential candidate for uncooled infrared sensor applications.

Bolometric properties of reactively sputtered TiO2−x films for thermal infrared image sensors

A heat-sensitive layer (TiO2−x) was successfully deposited by RF reactive magnetron sputtering for infrared (IR) image sensors at different relative mass flow of oxygen gas (RO2) levels. The deposition rate was decreased with an increase in the percentage of RO2 from 3.4% to 3.7%. TiO2−x samples deposited at room temperature exhibited amorphous characteristics. Oxygen deficiency causes a change in the oxidation state and is assumed to decrease the Ti4+ component on the surfaces of TiO2−x films. The oxygen stoichiometry (x) in TiO2−x films decreased from 0.35 to 0.05 with increasing the RO2 level from 3.4% to 3.7%, respectively. In TiO2−x−test-patterned samples, the resistivity decreased with the temperature, confirming the typical semiconducting property. The bolometric properties of the resistivity, temperature coefficient of resistance (TCR), and the flicker (1/ f) noise parameter were determined at different x values in TiO2−x samples. The rate of TCR dependency with regard to the 1/ f noise parameter is a universal bolometric parameter (β), acting as the dynamic element in a bolometer. It is high when a sample has a relatively low resistivity (0.82 Ω·cm) and a lower 1/ f noise parameter (3.16 × 10−12). The results of this study indicate that reactively sputtered TiO2−x is a viable bolometric material for uncooled IR image sensor devices.

Calculation of Temperature Coefficient of Resistance for Potential Barrier Structure for Bolometer in Uncooled Infrared Image Sensor

Calculation of Temperature Coefficient of Resistance for Potential Barrier Structure for Bolometer in Uncooled Infrared Image Sensor

Calculation of Temperature Coefficient of Resistance for Potential Barrier Structure for Bolometer in Uncooled Infrared Image Sensor

A potential barrier structure is a candidate for producing high temperature coefficient of resistance (TCR) devices. The electrical characteristics of such a structure for application in a bolometer for an infrared image sensor are calculated on the basis of a thermionic electron emission theory and the effect of tunneling through the barrier layer. The TCR is obtained using the resistivity dependence on temperature and depends mainly on the barrier height. The TCR value is derived as a function of the barrier height, barrier thickness, and bias voltage to the structure. To obtain a TCR of greater than 0.04/K, the barrier height must be more than 0.3 eV. The resistivity also depends on barrier height. The thickness of the barrier layer is also important because it affects the resistivity and TCR. Proper design of a potential barrier structure will yield a bolometer film having a high TCR and low resistivity.

The bolometric characteristic of thermally oxidized thin nickel film for an uncooled infrared image sensor

The resistivity of nano-scaled thin nickel film can be controlled so as to be applicable to MEMS-based micro-bolometric infrared image sensor technology. DC-sputtered 60 nm-thick thin nickel film on a SiO 2/Si substrate was oxidized in O 2 ambient. From XRD and electrical analyses, a phase transformation from the metallic nickel film to crystalline nickel oxide films was verified. The thin oxidized nickel films showed a negative TCR (temperature coefficient of resistance (above −3.22%/°C)) which is indicative of a semiconductor behavior. A 1/ f noise result ranging from 1 Hz to 100 Hz was also acquired.

Modulation-Doped Heterostructure-Thermopiles for Uncooled Infrared Image-Sensor Application

Novel thermopiles based on modulation doped AlGaAs/InGaAs, AlGaN/GaN, and ZnMgO/ZnO heterostructures are proposed and designed for the first time, for uncooled infrared image sensor application. These devices are expected to offer high performances due to both the superior Seebeck coefficient and the excellently high mobility of 2DEG and 2DHG due to high purity channel layers at the heterojunction interface. The AlGaAs/InGaAs thermopile has the figure-of-merit Z of as large as 1.1 × 10-2/K (ZT = 3.3 over unity at T = 300K), and can be realized with a high responsivity R of 15, 200V/W and a high detectivity D∗ of 1.8 × 109cmHz1/2/W with uncooled low-cost potentiality. The AlGaN/GaN and the ZnMgO/ZnO thermopiles have the advantages of high sheet carrier concentration due to their large polarization charge effects (spontaneous and piezo polarization charges) as well as of a high Seebeck coefficient due to their strong phonon-drag effect. The high speed response time τ of 0.9ms with AlGaN/GaN, and also the lower cost with ZnMgO/ZnO thermopiles can be realized. The modulation-doped heterostructure thermopiles presented here are expected to be used for uncooled infrared image sensor applications, and for monolithic integrations with other photon detectors such as InGaAs, GaN, and ZnO PiN photodiodes, as well as HEMT functional integrated circuit devices.

Poly(3,4-Ethylenedioxythiophene): Poly(Styrenesulfonate) (PEDOT:PSS) Films for the Microbolometer Applications

In this paper, Poly(3, 4-ethylenedioxythiophene): Poly (Styrenesulfonate) (PEDOT: PSS) thin films for application in a bolometer, a type of uncooled infrared image sensor, are presented. In addition, the TCR and 1/ƒ noise dependencies of PEDOT: PSS thin films on the thermal treatment conditions are demonstrated. It is also shown that an appropriate thermal treatment can suppress the 1/ƒ-> noise of PEDOT: PSS thin films while maintaining the resistivity and TCR. A high TCR value over -4%/°C (within 10ohm·cm) through chemical treatment is also presented. The results of this study show that PEDOT: PSS thin films have potential for use as a bolometric material.

A new dielectric bolometer mode of detector pixel for uncooled infrared image sensor with ferroelectric bst thin film prepared by metal-organic decomposition

A Ba1−xSrxTO3(Bi/Sr=75/25) ferroelectric thin film for detector pixel of uncooled infrared (IR) image sensor was prepared by metalorganic decomposition (MOD) with final annealing at 700 to 800°C. The films electrical characteristics such as temperature dependence of capacitance and insulation are very good from the viewpoints of spatial uniformity and stability against thermal cycling. The MOD film was applied to our proposed dielectric bolometer (DB) mode cf IR detector that has merits in 1) room temperature operation, 2) chopperless, 3) low power dissipation, and 4) high sensitivity. Finally, the DB-mode operation in the detector pixel was confirmed on the integrated device structure, and the resultant voltage sensitivity (Rv) and specific detectivity (D*) were observed to be 0.4 kV/W and 9.8×107 cmHzl/2/W with noise voltage (Vn) of 100 nV, respectively, where the detector size was 200μm2. Excellent output linearity against IR power down to 0.5 mW/cm2 and an IR image from IR source with average power of 6 mW/cm2. were also obtained.

Si monolithic microbolometers of ferroelectric BST thin film combined with readout FET for uncooled infrared image sensor

A silicon monolithic ferroelectric thin-film bolometer coupled with a readout FET has been developed for uncooled infrared imaging applications by means of Si-bulk micromachining and pulsed-laser-deposited (PLD) barium strontium titanate Ba 1− x Sr x TiO 3 (BST) thin films. It is a new type of dielectric bolometer (DB) mode based on the strong temperature dependence of capacitance upon the ferroelectric phase transition. The pixel circuit is a serial pair of capacitors where a sensing capacitor is fabricated on a thermally isolated membrane and a reference capacitor on bulk area. And a new pulse-biased-operation mode has been implemented to sense the voltage change at the interface node between sensitive and the reference capacitors. In order to avoid crack and deformation on the thermally insulated structure, a stress-balanced structure by multi-layered membrane has been adopted, where the ferroelectric capacitor is formed on a triple layer of NSG/SiN/SiO 2-stacked films. A BST (75/25) film on membrane is found to show positive temperature-coefficient of dielectric constant (TCD) ranging from 1 to 6%/K. Upon infrared irradiation on the membrane part, a capacitance difference arising from a temperature rise is significantly induced within the two capacitors. Thermal signals have been confirmed with one pixel bolometer tested under an infrared light irradiation. A new monolithic process flow is developed to combine an n-MOSFET process and a Si-bulk micromachining process, and ferroelectric capacitors on the stress-balanced membrane are able to be formed monolithically with MOSFETs for source-follower output buffer. The pixel structure also shows a simple configuration, and is very effective in reducing their pixel size and then increasing the pixel density. Finally, it is especially noted that the operation in the detector pixel in the DB mode is confirmed on the monolithically integrated device structure.

Detector pixel in dielectric bolometer mode based on ferroelectric thin film capacitors for uncooled infrared image sensor

Detector pixel in dielectric bolometer mode based on ferroelectric thin film capacitors for uncooled infrared image sensor