Steve Griggs, Judy Zhu, Winston Chan, David Chodelka, Peter Zalud, Tom Senko, David Hill, Wei Zhang, Lewis Haber, Zane Shellenbarger, Xiaohui Wang, Chris Parks, James Kim, Jim Andrews, Rob Farkas, Jesse Battaglia, John Tower, Namwoong Paik
Many Lidar system applications are best implemented with photon-counting sensors such as Geiger-mode avalanche photo diode arrays (GmAPD). To meet this emerging need, SRI has become a merchant supplier for custom GmAPD sensor arrays. SRI is currently building several different custom sensor chip assembly (SCA) designs for our customers. These entirely new sensors are based on our extensive GmAPD design and camera sensor manufacturing experience and designed to address lessons learned in the field. Our objective is to build GmAPD arrays that are truly ready for use in fielded mission critical systems. We report on our development of new ROICS and both planar and mesa type detectors at 1.0um and 1.5um and our packaging, assembly, and testing approach for these new single photon sensitive sensors.
KEYWORDS: Modulation transfer functions, Quantum efficiency, Electric fields, Silicon, Imaging systems, Reflection, Photon transport, Monte Carlo methods, Image sensors, Signal to noise ratio
This paper discusses specific SRI CMOS imagers that use for optimization a relatively new imaging performance parameter called the Contrast Detection Figure of Merit (CDFM). The large backside illuminated (BSI) stitched imagers come in two primary formats: a NMOS 10 um pixel x Mk x Nk imager where M x N are whole numbers and a PMOS 4um quad pixel x 4k x 4k and 8k x 8k. We briefly describe their pixel design and performance in addition to comparing NMOS and PMOS technologies discussing their advantages and disadvantages. Next we describe the CDFM technique where we join TCAD device and Monte Carlo simulations which together produce the modulation transfer function (MTF) and Quantum Efficiency (QE) as a function of photon wavelength, silicon epitaxial (epi) thickness and substrate bias given the pixel size. The two parameters are then multiplied together producing CDFM. The results show that quantum efficiency (QE) and the modulation transfer function (MTF) are competing variables which lead to an optimum epi thickness for maximum CDFM and contrast signal to noise (CSN) performance. The CDFM curves can also be expanded to MTFxQExBB where BB is the working Black Body radiation spectrum (BB) leading us to absolute performance given the strength of incoming radiation as a function of wavelength. Lastly, the paper compares CDFM modeling and testing results using standard measurement techniques (MTF, QE and Photon Transfer).
Technology developed for a 5.5 μm pixel interline transfer CCD family has been incorporated into a new family of highperformance 7.4 μm pixel CCDs, providing significant improvements in several key performance parameters compared to both the 5.5 μm family as well as the previous generation of 7.4 μm pixel products. Smear in the new platform has been reduced to -115 dB, and frame rate has been doubled relative to the previous generation of 7.4 μm pixel products. Dynamic range in normal operation has been improved to 70 dB, and the platform supports a new extended dynamic range mode which provides 82 dB when binning 2 × 2. The new family leverages the package and pin-out configurations used in the 5.5 μm pixel family, allowing easy integration into existing camera designs.
A new 5.5 &mgr;m pixel interline transfer CCD technology platform has been developed that offers significant improvements in performance while retaining the dynamic range, quantum efficiency, and responsivity available from the previous generation 7.4 µm pixel. Smear has been reduced to -100 dB, and a new quad-output architecture increases the maximum frame rate up to 120 fps for a 1 MPix sensor. This technology is now being deployed across a family of image sensors that share a common package and pin-out, facilitating faster camera design and product commercialization.
When interline CCD image sensors increase in size beyond 4 million pixels, CCD dark current begins to degrade the signal. Some scientific and photographic applications use very slow readout rates (less than 1 MHz) to reduce the noise level. At a 1-MHz readout rate, a 4-megapixel imager will take at least 4 s to read out. This extended time period allows a significant amount of dark current to build up and frustrate efforts to reduce noise. Often this situation leads to the additional expense of a low-temperature operation. The accumulation-mode readout method for interline CCD image sensors is being developed at Eastman Kodak Company. Previously, accumulation mode could only be applied to the full-frame architecture because the p-type substrate acted as a source for holes. Interline CCD image sensors with n-type substrates have no ready source of holes to accumulate the surface of the CCD under all phases. This problem has been overcome, allowing room-temperature operation without significant dark current generation.
CCD image sensors have been utilized as the detectors in digital spot mammography for needle biopsy systems. The requirements of a detector for this application are large sensing area, large pixel size, moderate resolution, and low noise. A large area full-frame CCD image sensor has been developed that is 50 mm X 50 mm with 2084 X 2084 pixels. It is manufactured using a true two-phase, transparent gate, buried channel CCD process. The transparent gate process improves the quantum efficiency from 40 percent to 55 percent at 540 nm. The true two-phase CCD operates in accumulation mode for low dark current without compromising charge capacity. The sensor has two different output amplifiers optimized for either low signal applications or high dynamic range applications. At a 2 MHz pixel rate the dynamic range is 84 dB or 88 dB depending on which output amplifier is selected. The large sensor format allows the elimination of the demagnification requirement in digital spot mammography applications and may be useful for mid-field digital diagnostic systems.
We are developing an L-band (1.3 GHz) high-current relativistic klystron (5 kA, 500 kV) for repetitive (200 pps) pulsing. We have designed and tested an extraction cavity that removes energy from the modulated electron beam and radiates it into an anechoic chamber in the TM01 mode. Peak power in excess of 450 MW has been measured for a single shot and 275 MW for a sustained burst producing 3.3 kW of average power. This klystron is now being transitioned to a long pulse (> 500 ns), single shot facility.
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