Abstract
The large imaging format, high sensitivity, compact size, and ease of operation of silicon-based sensors have led instrument designers to choose them for most visible-light imagers and spectrometers for space-based applications. This will probably remain the case in the near future. In fact, technologies presently under development will tend to strengthen the position of the silicon-based sensors. CCD-CMOS hybrids currently being developed may combine the advantages of both imagers and new high-gain amplifiers and could permit photon- counting sensitivity even in large-format imagers. Back- illumination potentially enables silicon detectors to be used for photometry and imaging applications for which front- illuminated devices are poorly suited. Successful detection by back illumination requires treatment of the back surface using techniques such as delta doping. Delta-doped CCDs were developed at the Microdevices Laboratory at the Jet Propulsion Laboratory in 1992. Using molecular beam epitaxy, fully- processed thinned CCDs are modified for UV enhancement by growing 2.5 nm of boron-doped silicon on the back surface. Named delta-doped CCDs because of the sharply-spiked dopant profile in the thin epitaxial layer, these devices exhibit stable and uniform 100% internal quantum efficiency without hysteresis in the visible and ultraviolet regions of the spectrum. In this paper we will discuss the performance of delta-doped CCDs in UV and EUV, applicability to electron- bombarded CCD (EBCCD), our in-house thinning capability, and bonding approaches for producing flat focal plane arrays. Recent activities on the extension of delta-doping to other imaging technologies will also be presented.
