26 April 2008 Correlating photodetector with current carrying photogate for time-of-flight distance measurements
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Abstract
Within this work a new correlating photodetector concept using current carrying photogates for Time-Of-Flight (TOF) based optical distance measurements is presented. The integrated photodetector consists of a PIN setup with a P+ doped anode, two N+ doped cathode fingers and a wide low doped intrinsic region in between. Furthermore a resistive polysilicon photogate is located in between of the readout cathode fingers on top of field oxide. Applying an electrical modulation signal to this photogate causes a linear potential drop along the resistor as a result of the control current. Therefore constant electric field is achieved in the photodetector regions below thus effecting photogenerated electrons to be directed to one or the other cathode, depending on the sign of the field. While positive charges are collected by the anode below, the modulation signal controls whether photocurrent of incident light is led to readout cathode 1 or 2. Due to this setup, applied modulation signals cause an optimal potential distribution for efficient correlation of ηsep=80% with incident optical signals. A responsivity of 0.23A/W {0.21A/W}, a rise time of 19.3ns {18.3ns} and a bandwidth of f-3dB=22.7MHz {29.6MHz} is measured at 660nm {850nm} together with low dark current of Idark<0.5pA. The capability of this photodetector is demonstrated at an integrated rangefinder chip in a range of 1.5m-3.5m achieving a standard deviation of σ<5cm at a white paper target and an optical power of Popt=1.5mW. A comparison of three realized photodetectors with different shapes of the photogate is done, each with an active area of 100μm×100μm and processed in 0.6μm BiCMOS.
© (2008) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
A. Nemecek, A. Nemecek, G. Zach, G. Zach, H. Zimmermann, H. Zimmermann, } "Correlating photodetector with current carrying photogate for time-of-flight distance measurements", Proc. SPIE 7003, Optical Sensors 2008, 70030L (26 April 2008); doi: 10.1117/12.780511; https://doi.org/10.1117/12.780511
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