1960197019011902003200 vity over wide ranges of temperature and background [6]. electrical contact for each element of a multielement array is W五 see Fig.20(a)]ofintrin Figl9.AimeincoftcevoltionofHeCeRtktectosndk HgCdTe detectors were (after Ref. allowed LWIR FLIR systems to operate with a single-stage nenmpoRypikaionofiHeCdephoadodesNas The simplest scanning linear FPA cons of arow of c high-speed age Is g d by scan ng the sc ross th laser system with HgCdTe photodiode.Howe ver.the hiel (detector Thes applicd anc n-type photoconductors used in the first generation 120 or 180 photoconductive elements depending on the Dewa nd gen:on FPA Detectors ewa Signal vdeo←-mmD Number of wires Number of driving ele Signal FPA Fig.20.(a)Scanning focal plane array (first generation)and(b)staring focal plane array (second generation). Opto-Electron.Rev.20.no.3.2012 A.Rogalski 291 photodiode was by Verie and Granger [65], who used Hg in−diffusion into p−type material doped with Hg vacancies. The first important application of HgCdTe photodiodes was as high−speed detectors for CO2 laser radiation [66]. The French pavilion at the 1967 Montreal Expo illustrated a CO2 laser system with HgCdTe photodiode. However, the high performance medium wavelength IR (MWIR) and LWIR linear arrays developed and manufactured in the 1970s were n−type photoconductors used in the first generation scan− ning systems. In 1969 Bartlett et al. [67] reported back− ground limited performance of photoconductors operated at 77 K in the LWIR spectral region. The advantage in mate− rial preparation and detector technology have led to devices approaching theoretical limits of responsivity and detecti− vity over wide ranges of temperature and background [68]. HgCdTe has inspired the development of the three “gen− erations” of detector devices (see Fig. 6). In the late 1960s and early 1970s, first−generation linear arrays [in which an electrical contact for each element of a multielement array is brought off the cryogenically−cooled focal plane to the out− side, where there is one electronic channel at ambient tem− perature for each detector element – see Fig. 20(a)] of intrin− sic photoconductive PbS, PbSe, HgCdTe detectors were developed. The first generation scanning system does not include multiplexing functions in the focal plane. These allowed LWIR FLIR systems to operate with a single−stage cryoengine, making the systems much more compact, lighter, and requiring significantly less power consumption. The simplest scanning linear FPA consists of a row of detec− tors. An image is generated by scanning the scene across the strip using, as a rule, a mechanical scanner. At standard video frame rates, at each pixel (detector) a short integration time has been applied and the total charges are accommo− dated. The US common module HgCdTe arrays employ 60, 120 or 180 photoconductive elements depending on the application. An example of 180−element common module FPA mounted on a dewar stem is shown in Fig. 21. Opto−Electron. Rev., 20, no. 3, 2012 A. Rogalski 291 Fig. 19. A time line of the evolution of HgCdTe IR detectors and key developments in process technology which made them possible (after Ref. 64). Fig. 20. (a) Scanning focal plane array (first generation) and (b) staring focal plane array (second generation)