The Study of Grating Structure Design and Focal Plane Array Process on Wide-Band Infrared Imaging Sensors

• Main Authors: CHEN,YI-KAI, 陳羿愷
• Other Authors: CHEN,ZI-JIANG
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/74404008646273706964

碩士 === 國防大學理工學院 === 光電工程碩士班 === 101 === In this thesis, we investigate the impacts of grating structure and focal plane array (FPA) process on the detective performance for long- and middle-wavelength infrared imaging sensors. For the grating structure, we optimize the grating period to improve the responsivity and the coupling efficiency from the theory analysis. Generally, the shorter grating period can result in the bigger diffraction angle for the incident infrared (IR) radiation so that the IR radiation can be absorbed effectively by the quantum well infrared photodetector (QWIP). However, if the grating period is shorter than the threshold length, the diffraction phenomenon will disappear and the incident infrared (IR) radiation will be reflected completely. Then, the QWIP absorbs no radiation and has the worse detective performance. The FPA process also significantly affects the detective performance for infrared imaging sensors. Therefore, we control the photoresist thickness and exposure time in the lithography process to transfer the grating structure exactly from the mask. The application of the lift-off resist in the metallization process can increase the stability and yield for the FPA. The contributions of this thesis are described as follows. Firstly, we design the optimal grating structure with the interference of the diffraction radiation from the theoretical perspective for the QWIP. Secondly, we provide a new process in the lithography and metallization to improve the quality of the grating structure and the yield of devices. Thirdly, we show that the grating depth and the bias voltage of the quantum well may shift the frequency of peak responsivity to higher or lower frequency with a given grating period. This principle can help designer control the desired frequency of peak responsivity precisely. Simulation results show that the optimal grating period is 2.75 μm in theory for the long-wavelength QWIP and the responsive critical dimension is 0.81 μm. In reality, the critical dimension has to be longer than 2 μm. Therefore, with 2 μm critical dimension, the optimal grating period is 6.9 μm. Our experiment results show that the grating period of 6.9 μm can improve 100% responsivity compared to that of 9.5 μm, when the grating depth is 0.89 μm.