Design of Low-Noise Output Amplifiers for P-channel Charge-Coupled Devices Fabricated on High-Resistivity Silicon - eScholarship

Design of Low-Noise Output Amplifiers for P-channel Charge-Coupled Devices Fabricated on High-Resistivity Silicon S. Haque a , F. Dion b , R. Frost b , R. Groulx b , S.E. Holland a , A. Karcher a , W.F. Kolbe a , N. A. Roe a , G. Wang a , and Y. Yu c a Lawrence b Teledyne Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA, USA 94720; DALSA Semiconductor, 18 Boul. de l’A´eroport, Bromont, Qu´ebec, Canada J2L 1S7; c Stanford University, 450 Serra Mall, Stanford, CA, USA 94305 ABSTRACT We describe the design and optimization of low-noise, single-stage output amplifiers for p-channel charge-coupled devices (CCDs) used for scientific applications in astronomy and other fields. The CCDs are fabricated on high- resistivity, 4000–5000 Ω-cm, n-type silicon substrates. Single-stage amplifiers with different output structure designs and technologies have been characterized. The standard output amplifier is designed with an n + polysil- icon gate that has a metal connection to the sense node. In an effort to lower the output amplifier readout noise by minimizing the capacitance seen at the sense node, buried-contact technology has been investigated. In this case, the output transistor has a p + polysilicon gate that connects directly to the p + sense node. Output structures with buried-contact areas as small as 2 µm × 2 µm are characterized. In addition, the geometry of the source-follower transistor was varied, and we report test results on the conversion gain and noise of the various amplifier structures. By use of buried-contact technology, better amplifier geometry, optimization of the amplifier biases and improvements in the test electronics design, we obtain a 45% reduction in noise, corresponding to 1.7 e − rms at 70 kpixels/sec. Keywords: Charge-coupled device, buried contact, noise, source follower, high-resistivity silicon 1. INTRODUCTION Charge-coupled devices (CCDs) are the detectors of choice for demanding scientific applications such as astron- omy and astrophysics. Large format, back-illuminated devices with high quantum efficiency and low noise form the basis for existing and planned large camera systems on astronomical telescopes such as the VLT Survey Telescope OmegaCAM 1 (268 Megapixels), the Dark Energy Survey camera 2, 3 (520 Megapixels), the Subaru HyperSuprime camera 4, 5 (872 Megapixels), the University of Hawaii Pan-STARRS camera 6, 7 (1.4 Gigapixels), and the camera for the planned Large Synoptic Survey Telescope 8 (LSST, 3.2 Gigapixels). Ideally the CCD read noise will be small in comparison to the shot noise from the background light levels in imaging applications. Given the desire to minimize the total time needed to read out the CCDs, e.g. 2 seconds for LSST, 8 it is necessary to reduce the CCD read noise in order to maintain shot-noise limited imaging at high readout rates since the CCD read noise increases as the square root of the pixel rate. 9 In addition, the signal can be photon-starved in spectroscopic applications in which case the read noise of the CCD output amplifier can be the major noise source. The emphasis of this paper is on the investigation of methods to reduce the CCD amplifier read noise for p-channel CCDs that are fabricated on high-resistivity silicon substrates. The organization of the paper is as follows. The background theory of CCD amplifier noise is presented, followed by a discussion of device design and technology developments that are investigated to improve the noise. This is followed by the description of experimental results measured on CCDs with varying amplifier designs. Further author information: (Send correspondence to S.H.) S.H.: E-mail: SHaque@lbl.gov, Telephone: 1 510 495 2965

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