Study On Integrated Polarization Near-infrared InGaAs Focal Plane Detectors

As one of the basic properties of light,polarization can provide another kind of information about the object that is different from its radiation intensity.Different objects or different states of the same object may produce different polarization states when emitting or reflecting infrared radiation.Therefore,it can improve image contrast and enhance the system's ability to detect and identify targets by detecting polarization signals in infrared imaging scene.Meanwhile,with the continuous advancement of preparation technology for InGaAs detector and micro-nano processing technology,it has become possible to use an on-chip integrated process to fabricate a near-infrared division of focal plane polarization detector.Based on the development needs of the integration and miniaturization of the near-infrared focal plane detector,the structure design,preparation process and characterization method of the integrated polarized InGaAs focal plane detector were studied.The main research contents and innovations involved are as follows:1.A simulation model suitable for the integrated polarization grating on the back-side illumination InGaAs detector chip was established.The FDTD solutions software was used to define the structure parameter range of the aluminum grating suitable for the near-infrared band to achieve higher TM wave transmittance and extinction ratio.The effect of structural parameter deviation on the polarization performance of the grating was analyzed.The results show that the deviations from grating period and duty cycle has a significant effect.When the gap between adjacent gratings is wider than the designed value,the blocking effect for TE wave is weakened,resulting in a significant reduction of extinction ratio.2.The performance test systems for the integrated polarization InGaAs focal plane detector were designed and built.The characterization methods were clarified to measure the response spectrum and blackbody response signal of conventional pixels and polarized pixels.In terms of polarization performance characterization,the test method of grating transmittance under three conditions were proposed,including the certain wavelength,variational wavelength and wide spectrum band.In particular,monochromatic circularly polarized light was used as the light source for the certain wavelength test to obtain more accurate test results.3.Two methods for on-chip integration of metal gratings on InGaAs focal plane detector were obtained.Firstly,the integrated method based on focal plane detector was proposed.After thinning the In P substrate and depositing a dielectric layer,the alignment marks were made on the back of the photosensitive chip according to the position of the lithographic marks on the readout circuit.Then based on these marks,the on-chip integration of the metal grating was completed by electron beam lithography and metal lift-off processes.Second,the integration process combined with the preparation process of InGaAs detector was proposed.The back registration process was introduced to make the alignment mark on the back of the chip.The etching process was adopted to prepare the metal grating by using the photoresist as a mask.The flip-chip bonding with the readout circuit was completed after the indium bumps were grown.At the same time,many key processes involved in the above methods were studied and improved.4.A back-side illumination NIR InGaAs polarization detector on-chip integrated with 64×64 superpixel metal grating was designed and successfully prepared.The grating morphology and detector performance were comprehensively characterized and analyzed.The peak detectivity of the four angle polarimetric pixels exceeds 1.5×10¹²cm?Hz^1/2/W,but the average extinction ratio reaches only 4.The effect of alignment deviation introduced by the fabrication process on the polarization performance of the detector was further studied.It was found that the alignment deviation significantly increased the TE wave transmittance of the polarimetric pixel,which becomes a key factor affecting its extinction ratio.The result provides a technical way for the subsequent improvement of the extinction ratio of the integrated polarization detector.5.The InGaAs detector integrated with linear-array polarization grating was creatively designed to meet the requirements of push-broom applications of polarization imaging.The four angle gratings each cover a row of photosensitive elements and extend 5?m to ensure that the underlying photosensitive elements are completely covered.In order to maintain a good grating shape,the adjacent 0°gratings have 1?m spacing in the lateral direction.Finally,the on-chip integration of a 540×4linear-array polarization grating was achieved.The test results show that the peak detectivity of the polarization pixels exceeded 1.05×10¹² cm?Hz^1/2/W and the extinction ratio reached 21.This verified the effect of alignment deviation control to improve the extinction ratio of the integrated polarization detector.