The metal-type microbolometers in CMOS technology normally suffer low resistivity and high thermal conductivity, limiting their performance and application areas. In this paper, we demonstrate a polysilicon microbolometer fabricated in 0.18 µm CMOS and post-CMOS processes. The detector is composed of a SiO2 absorber coupled with a salicided poly-Si thermistor that has a high resistivity of 1.37×10−4 Ω·cm and low thermal conductivity of 18 W/m·K. It is experimentally shown that the microbolometer with a 40 µm × 40 µm pixel size has a maximum responsibility and detectivity of 2.13×104 V/W and 2.33×109 cmHz1/2/W, respectively. The results are superior to the reported metal-type and diode-type microbolometers in the CMOS process and provide good potential for a low-cost, high-performance, uncooled microbolometer array for infrared imaging applications.
Microbolometers based on the CMOS process has the important advantage of being automatically merged with circuits in the fabrication of larger arrays, but they typically suffer from low detectivity due to the difficulty in realizing high-sensitivity thermistors in the CMOS process. In this paper, two resistive microbolometers based on polysilicon and metal Al thermistors, respectively, are designed and fabricated by the standard CMOS process. Experimental results show that the detectivity of the two resistive microbolometers can reach a maximum of 1.78 ´ 109 cmHz1/2/W at 25 μA and a maximum of 6.2 ´ 108 cmHz1/2/W at 267 μA. The polysilicon microbolometer exhibits better detectivity at lower bias current due to its lower effective thermal conductivity and larger resistance. Even though the thermal time constant of the polysilicon thermistor is three times slower than that of the metal Al thermistor, the former is more suitable for designing a thermal imaging system with sensitive and low power consumption.
The resistive microbolometer fabricated by using CMOS technology can be monolithically integrated with the readout circuit but usually performs poorly in responsivity and detectivity. In this paper, the poly-Si microbolometer with Al grating structure is demonstrated in the standard CMOS process. The simulation results show that not only are surface plasmon polaritons generated at the interface of the Al grating and SiO2, Al grating also provides the infrared resonant cavity required for the absorber, which improves the responsivity of the microbolometer. According to the experimental results, the maximum detectivity of the microbolometer with the grating structure reaches up to 2.2610 9 cmHz 1/2 /W at 10 μm, which means an increase by 27.8% compared to the one without the Al grating. Moreover, the average detectivity of the microbolometer is also improved when the wavelength ranges from 7 μm to 13 μm. It is effortless to implement the proposed high-performance microbolometer in a unit structure based on CMOS technology, which is favorable to high-density array integration.
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