Fabrication Of Microbolometers Research Articles

Characterization of platinum and titanium thermistors for terahertz antenna-coupled bolometer applications

Microbolometer is a radiation detector for infrared (IR) and terahertz (THz) waves. The temperature coefficient of resistance (TCR) of the thermistor is a vital factor, as the responsivity is proportional and noise equivalent power (NEP) is inversely proportional to it. The narrow-width effect on TCR and resistivity on two different substrates (SiO2/Si and SiNX/SiO2/Si) for platinum (Pt) and titanium (Ti) thermistor with various design width (DW) = 0.1–5 μm are investigated. Increased resistivity and reduced TCR of the devices with the decreased line width, is observed commonly for both metal and fitted with empirical formulae, which hold well for different substrates. It is evident from electron backscatter diffraction (EBSD) results showing reduced average grain size form Ti film to Ti nanowire (DW = 0.1 μm), that the reduced TCR is not dependent on crystal orientation or phase variation of material but can be correlated with reduced grain size due to reduction of width. The optimum value considering design requirement, thermistor of DW = 0.1 μm and 0.2 μm is used further for the fabrication of microbolometers. It is found that the device with DW = 0.1 μm of Ti thermistor has ∼1.5 times higher electrical responsivity (376 V/W) at maximum allowable current than that with DW = 0.2 μm (254 V/W), which is also ∼11 times higher than device with DW = 0.1 μm of Pt thermistor.

Thin film uncooled microbolometers based on plasma deposited materials

We make a summary of our research and development efforts made about microbolometers (MBs) based on plasma-enhanced chemical vapor deposition (PECVD) materials, like noncrystalline semiconductors that provide high temperature coefficient of resistivity values, in conjunction with SiOx and SiNx dielectrics used for thermoisolation, which, together with micromachining, are paving new ways for fabrication of MBs, making them promising for 2D imagers in both infrared and tera-Hertz regions. We studied a-Si:H(B), a-Ge:H, a-GeSi:H, and polymorphous p-Ge:H, p-SiGe:H as thermosensing materials (TSMs) for MBs in “bridge” configuration with “planar” and “sandwich” electrodes. This allows placing the read-out circuitry under the bridge, improving use of pixel area. PECVD SiNx films were used as both a support layer and as a coating for improving the response for λ = 8–12 μm. 2D modeling revealed both linear and super linear response to IR intensity. Voltage responsivity RU = (1.2–7) × 105 V/W is observed in both “planar” and “sandwich” MBs. The latter shows current responsivity RI = 0.3–14 A/W higher by about three orders of magnitude than the former. A key issue for any detector is the detectivity. Different TSMs show different noise characteristics. Noise in “sandwich” MBs is several orders of magnitude higher than that in “planar” structures. The best parameters observed with TSM Ge-Si:H are: RU = 7.2 × 105 V/W, RI = 14 A/W voltage and current detectivities [Formula: see text] = 8 × 109 cm Hz1/2W−1 and [Formula: see text] = 4 × 109 cm Hz1/2W−1. Junction structures on top of the “bridge” are also discussed. Finally we describe some reported applications of MBs.

Terahertz metamaterial absorbers with an embedded resistive layer

A conductive layer of Ti, with a sheet resistance of about 220 Ω/sq, was placed in the dielectric spacer of an Al/SiOx/Al metamaterial terahertz absorber at various depths to probe the effect on the absorption of terahertz radiation. For a square size of 15 µm and a periodicity of 21 µm, and dielectric thickness approximately 1.6 µm, maximum absorption was 60%, 88%, and 94% for Ti layers 297, 765, and 1270 nm deep into the SiOx. Finite element simulations of the absorption correlated well with that of the measurements. This indicates that metamaterials with an embedded high temperature coefficient of resistance (TCR) conducting layer can be used for fabrication of microbolometers with tuned spectral sensitivity.

Strong terahertz absorption using SiO2/Al based metamaterial structures

Metamaterial absorbers with nearly 100% absorption in the terahertz (THz) spectral band have been designed and fabricated using a periodic array of aluminum (Al) squares and an Al ground plane separated by a thin silicon dioxide (SiO2) dielectric film. The entire structure is less than 1.6 mm thick making it suitable for the fabrication of microbolometers or bi-material sensors for THz imaging. Films with different dielectric layer thicknesses exhibited resonant absorption at 4.1, 4.2, and 4.5 THz with strengths of 98%, 95%, and 88%, respectively. The measured absorption spectra are in good agreement with simulations using finite element modeling.

차량 내 탑승자 상태 인식용 적외선 센서의 제조 및 특성

A noble infrared sensor was studied for passenger conditional detection in vehicle, This research relates to uncooled infrared sensors for detecting the presence, type and temperature of occupants in vehicle. It sense that the occupants purpose to control the smart airbag for safety in the case of adult or child and to control the automatic air conditioning for convenience. This paper described the design and the fabrication of microbolometers which were composed of 2 by 8 elements using the surface micromachining technology. The characteristics of the array were investigated in the spectral region of <TEX>$8{\sim}12{\mu}m$</TEX>. The fabricated detectors exhibited the thermal mass of <TEX>$7.05{\times}10^{-9}\;J/K$</TEX>, the thermal conductance of <TEX>$1.03{\times}10^{-6}\;W/K$</TEX>, the thermal time constant of 6.8 ms, the responsivity of <TEX>$2.96{\times}10^4\;V/W$</TEX> and the detectivity of <TEX>$1.01{\times}10^9\;cmHz^{1/2}/W$</TEX>, at the chopper frequency of 10 Hz and the bias current of <TEX>$4.4{\mu}A$</TEX>. We could successfully detect the human body condition in the divided zone. As a results, we concluded that microbolometer optimized in this research could be useful for the application of passenger conditional detection in vehicle.

IR bolometers based on amorphous silicon germanium alloys

In this work, we report the fabrication and characterization of bolometers based on amorphous silicon germanium alloys (a-Si 1 − x Ge x :H,F). The fabrication of microbolometers with thermally isolated a-SiGe thin film as sensing layer, is described. Membrane-supported and bridge-supported detectors have been fabricated. Sensing layer is deposited by low frequency plasma enhanced chemical vapor deposition technique. Since this deposition is carried out at relative low temperature T D=573 K, the read-out IC fabricated on silicon substrate is not affected, providing compatibility with silicon IC technologies. Responsivity and detectivity were measured under illumination at different bias voltages. The thermal time constant, the thermal conductance and current noise are determined by means of the voltage–time curves. Responsivity and detectivity are observed to depend on the physical properties of the materials forming the device and on the device geometry. Obtained results of pixel resistance, thermal resistance and responsivity demonstrate a-SiGe:H,F like a material suitable for realizing high-performance microbolometers.