During microbolometer operation, the detector occasionally views high temperature scenes such as the sun or
flames at very close distance. The detector temperature can then increase to a level so high that the sensing material
experiences an annealing effect. Accordingly, the microbolometer is required to stand high temperatures that can cause
In this paper, a bimorph leg integrated microbolometer structure is proposed. The bimorph leg is an extra leg that
is separated from the signal transfer legs. It is bent downward and snaps onto the substrate when the microbolometer's
temperature reaches a critical temperature. The temperature of the micro-bolometer is then decreased as heat is
transferred to the substrate.
By snapping the bimorph leg down onto the substrate, the microbolometer's thermal conductance is temporarily
increased roughly three-fold higher than that of the normal state and thermal damage to the bolometer material can be
effectively prevented. The increase of thermal conductance can be controlled by changing the size of the bimorph leg.
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 SiO2 only layer (thermal insulation leg) assures thermal conductance of 1.06x10-7W/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 SiO2 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.
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 SiO2: 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 SiO2, 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 SiO2 (10μm x 2μm x 0.2μm), the device can have low thermal conductance of 1.3x10-7W/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.