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A novel JFET readout structure applicable for pinned and lateral drift-field photodiodes

: Süss, Andreas; Hosticka, Bedrich J.


Berghmans, Francis (Hrsg.) ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
Optical Sensing and Detection II : 16-19 April 2012; Brussels, Belgium
Bellingham, WA: SPIE, 2012 (Proceedings of SPIE 8439)
ISBN: 978-0-8194-9131-2
Paper 84391D
Conference "Optical Sensing and Detection" <2, 2012, Brussels>
Fraunhofer IMS ()
JFET; pinned photo diode (PPD); Lateral Drift-Field Photodetector (LDPD); readout structure; noise; CPS; APS; RTS noise; flicker noise

Enhancement of the dynamic range of photodetectors used in advanced image sensors such as time-of-flight sensors or image sensors for automotive applications is a major research topic. In this paper an improved unipolar readout structure is presented, that is superior to the widely employed source follower readout implemented by enhancement MOSFETs. It yields a high output voltage swing and low noise, while requiring no additional processing steps. The readout structure is consisting of a low-noise JFET whose gates are formed by a floating diffusion, thus preserving in-pixel accumulation capability - which additionally improves noise performance. This structure outperforms a simple in-pixel implementation of a JFET and a photodetector in terms of the necessary area consumption, thus improving fill factor. For pixels with a pitch of several microns this readout structure is a good trade-off between area, output voltage swing and, most important, noise performance. Furthermore, since only a ground connection is needed for application, fill-factor and power-grid disturbances like DC-voltage drop can be additionally improved.