An infrared (IR) transparent window is necessary for the IR sensor package. The most commonly used materials for IR transparent window are germanium (Ge) and silicon (Si). Ge has excellent optical properties but also the disadvantage of expensive price. Si has merits such as inexpensive cost and CMOS process compatibility but it has lower transmittance in the range of LWIR region than Ge. Therefore, an alternative anti-reflection (AR) coating is necessary to increase the transmittance of Si as an IR transparent window in the LWIR region. A simple single layer antireflection coating was newly designed on the silicon window for the infrared sensor package. Among the various materials, nickel oxide (NiO) was selected as an AR coating material due to its suitable optical properties and simple process. NiO film was deposited onto the double sided polished Si wafer by reactive rf sputtering with Ni target in an environment of Ar and O2 mixed gas. The thickness of the NiO film was determined by Essential Macleod simulation. FT-IR was used to measure the transmittance of the samples in the LWIR region. After the nickel oxide film was sputtered onto the double sides of the silicon wafer, the measured transmittance of the Si wafer was increased over 20% in the LWIR region compared with that of uncoated Si wafer. Additionally, annealing effect on the transmittance of NiO coated Si wafer was studied. By increasing the annealing temperature from 300° to 700°, an additional increase of transmittance was achieved.
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.
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 O2/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 8.5×10-13 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.
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 Impact-Echo (IE) method has been widely used to evaluate the integrity of concrete structures. In this method, the P- wave velocity of concrete is a crucial parameter in determining the thickness of concrete lining and the location of cracks or other defects. In this paper, Spectral Analysis of Surface Wave (SASW) method was employed to determine P-wave velocity of concrete, and IE-SASW method was suggested by combining two nondestructive testing methods. IE method was used for the detailed nondestructive evaluation of concrete whereas SASW method was employed for the measurement of the average P-wave velocity and for the status evaluation of concrete. The feasibility study of IE-SASW method was performed by using finite element method. Experimental studies were also performed in the slab type concrete model specimens in which various types of defects or boundaries were included at known locations. SASW tests showed the potential of determining the P-wave velocity of concrete accurately and IE tests were able to determine the thickness of structures and locations of defects. Based on both experimental and numerical studies, the feasibility of the proposed method was verified.