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Proceedings Paper

CMOS position-sensitive photodetectors (PSDs) for integrated sensor systems
Author(s): Anssi Jaakko Maekynen; Harold Benten; Tarmo Ruotsalainen; Timo E. Rahkonen; Juha Tapio Kostamovaara
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Paper Abstract

Implementations and test results of one single-axis and 2- axis CMOS PSDs as well as a BiCMOS integrated receiver channel are presented. The single-axis PSD has a conventional LEP structure. It uses the well-substrate junction as a photodetector and pinched well as current dividing layer. An interelectrode resistance, NEP and position sensing accuracy of 152 k(Omega) , 1.6 pW/(root)Hz (850 nm) and 0.1%rms are achieved with the detector measuring 5 X 0.2 mm2. The first 2-axis PSD is a tetralateral LEP but instead of having strip-like continuous edge-electrodes it has electrodes composed of 100 discrete contacts, each of which is connected to the output current line using MOS switches. Linear position response is provided by disconnecting one opposite pair of the electrodes from preamplifier inputs and measuring one dimension at a time. An interelectrode resistance, NEP and accuracy of 4.5 k(Omega) , 10 pW/(root)Hz and 0.07%rms were achieved with this PSD using the alternate measurement mode. The second 2-axis PSD has an operating principle similar to a basic LEP but is composed of an array of phototransistors and polysilicon resistors. The NEP and position sensing nonlinearity of the sensor were 0.5 pW/(root)Hz and 0.04%rms, respectively. The third 2-axis PSD has the same construction as the second one but the phototransistors and polysilicon resistors were replaced with well-substrate photodiodes and pmos transistors, respectively. By driving one or more adjacent transistors in off-state the LEP mode can be changed to a segmented PSD mode providing the means to combine the high lateral sensitivity of the segmented mode with the large and linear measurement fields of the LEP. The BiCMOS receiver channel is composed of a transimpedance preamplifier, voltage amplifiers, gain control and offset cancellation blocks and a synchronous detector. The transimpedance at four different gains for a signal frequency ranging typically from 5 kHz to 10 kHz were 7 M(Omega) , 33 M(Omega) , 143 M(Omega) and 488 M(Omega) . The measured noise current density was lower than 0.3 pA(root)Hz, and the area and power consumption were 2.9 X 0.45 mm2 and 37 mW, respectively. As the achieved results fulfill the demands set for a typical signal conditioning channel of a PSD sensor system, the properties appear to be suitable for integrated PSD systems.

Paper Details

Date Published: 25 September 1997
PDF: 12 pages
Proc. SPIE 3100, Sensors, Sensor Systems, and Sensor Data Processing, (25 September 1997); doi: 10.1117/12.287729
Show Author Affiliations
Anssi Jaakko Maekynen, Univ. of Oulu (Finland)
Harold Benten, Univ. of Oulu (Finland)
Tarmo Ruotsalainen, Univ. of Oulu (Finland)
Timo E. Rahkonen, Univ. of Oulu (Finland)
Juha Tapio Kostamovaara, Univ. of Oulu (Finland)


Published in SPIE Proceedings Vol. 3100:
Sensors, Sensor Systems, and Sensor Data Processing
Otmar Loffeld, Editor(s)

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