CMOS图像传感器常采用像元在奈奎斯特频率处的调制传递函数(MTF)值对成像质量进行评价。MTF主要由孔径MTF和扩散MTF的频域乘积得到,其中孔径MTF与CMOS图像传感器像元的物理结构相关,扩散MTF主要由感光区p-n结的工艺参数决定,同时工艺参数会影响像元的量子效率(QE),进而影响信噪比(SNR)。从CMOS图像传感器像元的工艺参数出发,详细分析了MTF函数和SNR的理论机理,并列举了300~1000 nm光谱段中8个典型光波长条件下CMOS图像传感器像元的MTF和SNR的计算结果,L型灵敏度孔径的像元在奈奎斯特频率处的孔径MTF为固定值0.67,奈奎斯特频率处的扩散MTF随入射光波长的变大而减小,QE在800 nm入射光波长条件下达到峰值85.8%,而相同读出噪声和暗电流条件下的SNR也在800 nm处达到峰值124。

The modulation transfer function (MTF) value of complementary metal-oxide-semiconductor (CMOS) image sensors pixels at Nyquist frequency is typically used to evaluate the imaging quality. The MTF is mainly calculated by taking the frequency domain product of the aperture MTF and the diffusion MTF. The aperture MTF is determined by the physical structure of the CMOS image sensor pixel, whereas the diffusion MTF is determined primarily by the process parameters of the p-n junction in the photosensitive region. Simultaneously, the process parameters will affect the quantum efficiency (QE) of pixels, which will then affect the signal-to-noise ratio (SNR). The theoretical mechanism of MTF function and SNR is examined in detail in this paper, and the calculation results of MTF and SNR of CMOS image sensor pixels under 8 typical optical wavelengths in the 300--1000 nm spectral band are listed. The MTF of the pixel with L-shaped sensitivity aperture at Nyquist frequency is fixed at 0.67, the diffusion MTF at Nyquist frequency decreases as incident light wavelength increases, the peak value of QE is 85.8% at 800-nm incident light wavelength, and the peak value of SNR is 124 at 800 nm under the same reading noise and dark current.