Research On Microbolometers Based On Standard Integrated Circuit Technology

Microbolometer is a crucial part of infrared thermal imaging technology and plays an important role in fire detection,safety system and medical diagnosis.The microbolometer based on standard integrated circuit technology has the characteristics of high integration,low cost,small size,low power consumption and wide spectral response.It is an important development direction of infrared thermal detectors in the future.However,at present,such detectors have outstanding problems such as poor performance and poor imaging quality at room temperature.In this paper,two types of resistance-based microbolometers are designed and fabricated using integrated circuit technology,and their performance and structure optimization are studied.The main research contents and results are as follows:?1?Using 0.18?m standard CMOS technology,the resistance-based microbolometer integrated with silicide polysilicon material was designed and fabricated for the first time.Compared with common metal materials,silicide polysilicon materials have the advantage of high resistivity.The designed microbolometer uses silicide polysilicon as the thermistor material,SiO₂ dielectric as the infrared absorption material,and has a microbridge structure with two support arms.FDTD simulation results show that increasing the thickness of the SiO₂ absorber and integrating the Si₃N₄ layer on the surface can improve the infrared absorptance of the device,while reducing the thickness of the microbridge structure can reduce the thermal conductivity and thermal time constant of the device.Experiments were conducted on the microbolometer fabricated by the standard process and the Post-CMOS process.The results show that the designed device had a resistance of 52k?and a TCR of 0.335%/K.At 11.4?m,the device's maximum voltage responsivity R_V is 2065V/W,the noise voltage V_n is 5.03?V@0.21V,and the detectivity D^*is 2.12×10⁹ cm Hz^1/2/W@5?A,reaching the industry leading level.?2?Using 0.18?m standard CMOS technology,the Al resistance microbolometer with grating structure was designed and fabricated for the first time,for the microbolometer with the grating structure 22 times improvement on detectivity was achieved compared to the microbolometer without the grating structure.The device uses Aluminum as a thermistor,Si₃N₄ and SiO₂ as infrared absorbing materials,and has an L-shaped micro-bridge structure.The designed Al grating coupling structure is used to improve the infrared absorption efficiency of the detector.The FDTD simulation results show that the Al grating and the upper Si₃N₄ layer form a reflective cavity structure,and then the infrared light is reflected by the Al grating and thus is repeatedly absorbed by the Si3N4layer.Designing the width of the Al grating can increase the total infrared absorption and The maximum improvement can reach 30%@8?m.Experiments were conducted on the microbolometer prepared by the standard process and the Post-CMOS process.The results showed that the resistance of the designed device is 327.04?,and the TCR is 0.354%/K.Wthin measured bias range,the current responsivity R_I of the device with grating structure is much higher than that of the device without grating,and the enhancement can be up to 12.2 times@0.2V.The detectivity D^*of the device with grating structure is higher than that of the device without grating,and the maximum improvement can be up to 21.5 times@0.2V.