Silicon-Integrated Uncooled Infrared Detectors: Perspectives on Thin Films and Microstructures

Technologies for silicon process integration of infrared (IR) detector systems are driven by pursuits of low cost and high performance that are required for commercial viability. The high device yields that are commonplace in standard silicon integrated circuit (IC) manufacture are very attractive when applied to fabricating optoelectronic components with comparably superior uniformity and yield. Infrared photodetector technologies based on quantum detection in semiconductors or bolometric detection (thermoresistors, including transition-edge superconductors) have used cryogenic cooling by either Peltier effect or Joule–Thompson refrigeration for optimum low signal sensitivity at wavelengths beyond the near IR (λ 1.5 μm). Schottky-barrier focal plane array detectors, for example, have been developed for multiple wavelength imaging pyrometry systems for military and civilian applications. Uncooled technologies with reduced photon sensitivity are also of value in systems requiring small physical dimensions, lightweight, reduced complexity, and low component cost. Uncooled detectors (operating at ambient and near-ambient temperature, regulated and unregulated) based on silicon are considered in this paper. In telecommunications, IR detectors operating at optical fiber band passes at 1.3 μm and 1.55 μm are needed for photoreceivers and transreceivers. For massively parallel duplex data links, optical interconnects require small area and low power IR detector arrays operating at terabit/second system rates. Uncooled focal plane arrays are used to produce low-cost and lightweight IR cameras for night vision, security, motion sensing, law enforcement, thermal imaging, medical, machine vision, firefighting, inspection, forward-looking IR radar, transportation, unmanned airborne vehicles, rescue operations, meterology, and numerous other applications. Infrared detector technologies employ several principles, including photovoltaics, photoconductors, Si and Ge devices, microbolometers, pyroelectrics, and micromechanics. For high-speed mid-IR devices (e.g., 8–12 μm, 10 Hz), inter-sub-band transitions in quantum well IR photodetectors (QWIPs) are operated at cryogenic temperatures to suppress dark current or uncooled with heterodyne or photovoltaic detection. At longer wavelengths, IR camera technologies are being adapted to extend their sensitivities beyond the IR into the terahertz region for see-through object detection, security, and defense applications. This paper will briefly review the application areas of communications receivers and IR focal plane arrays from the perspective of meeting challenges posed by thin-film structures in IR detectors.