Orthogonal transfer array CCDs were originally developed by the University of Hawaii and MIT Lincoln Laboratory
for use in the focal planes of the ground-based Panoramic Survey Telescope and Rapid Response System
(Pan-STARRS). These devices have relatively large area (5x5 cm) and a novel, multiple-output readout architecture
that makes them attractive for certain applications in spaced-base X-ray astronomy. We have therefore
conducted a series of tests to determine their sensitivity to proton radiation encountered on-orbit. We report
effects of typical on-orbit proton exposure on charge transfer efficiency, dark current, noise and spectral resolution
as a function of device operating temperature and readout parameters.
The Pan-STARRS project has completed its first 1.4 gigapixel mosaic focalplane CCD camera using 60 Orthogonal Transfer
Arrays (OTAs). The devices are the second of a series of planned development lots. Several novel properties were
implemented into their design including 4 phase pixels for on-detector tip-tilt image compensation, selectable region logic
for standby or active operation, relatively high output amplifier count, close four side buttable packaging and deep depletion
construction. The testing and operational challenges of deploying these OTAs required enhancements and new approaches
to hardware and software. We compare performance achieved with that which was predicted, and discuss on-sky results,
tools developed, shortcomings, and plans for future OTA features and improvements.
Recent development efforts on the orthogonal transfer array (OTA) for the Pan-STARRS gigapixel camera 1 (GPC1) are described. A redesign of the prototype OTAs has been completed, and fabrication and packaging of the devices for the GPC1 are nearly complete. We briefly review the final design features and the resolution of the performance issues that arose in the first prototype devices. We then describe the packaging of the device and the challenges arising in achieving the necessary flatness at the device operating temperature. Plans and schedule for deploying focal-plane arrays of these devices are described.
The orthogonal-transfer array (OTA) is a new charge-coupled device (CCD) concept for wide-field imaging in groundbased astronomy based on the orthogonal-transfer CCD (OTCCD). This device combines an 8×8 array of small OTCCDs, each about 600×600 pixels with on-chip logic to provide independent control and readout of each CCD. The device provides spatially varying electronic tip-tilt correction for wavefront aberrations, as well as compensation for telescope shake. Tests of prototype devices have verified correct functioning of the control logic and demonstrated good CCD charge-transfer efficiency and high quantum efficiency. Independent biasing of the substrate down to -40 V has enabled fully depleted operation of 75-μm-thick devices with good charge PSF. Spurious charge or "glow" due to impact ionization from high fields at the drains of some of the NMOS logic FETs has been observed, and reprocessing of some devices from the first lot has resolved this issue. Read noise levels have been 10 - 20 e-, higher than our goal of 5 e-, but we have identified the likely sources of the problem. A second design is currently in fabrication and uses a 10-μm pixel design resulting in a 22.6-Mpixel device measuring 50×50 mm. These devices will be deployed in the U. of Hawaii Pan-STARRS focal plane, which will comprise 60 OTAs with a total of nearly 1.4 Gpixels.
The orthogonal-transfer array (OTA) is a new CCD architecture designed to provide wide-field tip-tilt correction of astronomical images. The device consists of an 8x8 array of small (~500x500 pixels) orthogonal-transfer CCDs (OTCCD) with independent addressing and readout of each OTCCD. This approach enables an optimum tip-tilt correction to be applied independently to each OTCCD across the focal plane. The first design of this device has been carried out at MIT Lincoln Laboratory in support of the Pan-STARRS program with a collaborative parallel effort at Semiconductor Technology Associates (STA) for the WIYN Observatory. The two versions of this device are functionally compatible and share a common pinout and package. The first wafer lots are complete at Lincoln and at Dalsa and are undergoing wafer probing.
In this paper we describe a new technology which fabricates CCDs and fully depleted silicon on insulator CMOS circuits on the same 150-mm silicon wafer. We present results from 7.5 X 7.5-micrometers 2 and 15 X 15-micrometers 2-pixel imagers that are 512 X 512 frame transfer devices. The 7.5-micrometers -pixel device exhibits a charge handling capacity in excess of 100,000 electrons at 3.3 V and the 15-micrometers - pixel device exhibits a charge-transfer efficiency over 99.998%. In addition, we demonstrate functional SOI CMOS ring oscillators with delay of 47 ps/stage at 3.3 V and 68 ps/stage at 2 V.
We describe the development at Lincoln Laboratory of large-area CCD imager arrays for soft x-ray astronomy. One such array consists of four, closely abutted, 420 X 420-pixel CCDs for the ASCA (formerly Astro-D) satellite that was launched on February 20, 1993. The CCDs were fabricated on p-type 6500-(Omega) -cm material in order to attain the deep depletion depths needed for the higher-energy (> 4 keV) photons. The use of high- resistivity material and the effects of space-radiation are among the principal technical issues which will be discussed. We are also developing the next-generation CCD sensors for the Advanced X-ray Astrophysics Facility which is currently scheduled for launch in 1998. This mission will use two multichip focal planes comprising ten chips, each of a larger format (approximately 1000 X 1000 pixels). In addition to a new CCD, this program will require other technology developments such as an innovative packaging method for the nonplanar focal planes.
focusing on work on large device formats, improvements in quantum efficiency, and reduction of CCD degradation in the natural space-radiation environment. Research was based on a 420 x 420-pixel frame-transfer device and a new 1024 x 1024-pixel device. To obtain high quantum efficiency from the visible into the UV, a technology for making back-illuminated versions of these devices is being developed. Quantum efficiencies greater than 80 percent in the 500-800 nm band have been obtained with a SiO antireflection coating. Particular attention is given to the problem of charge-transfer inefficiency degradation caused by energetic protons in space-based systems. It is shown that CCDs can be significantly hardened to radiation effects by a combination of special buried channel potential profiles and operation at temperatures around 150 K, where the trap sites created by the protons have emission times much longer than the clock periods.