Patent GB-1282117-A (GB)
Title: Infra-red spectrometer using integrated mos elements
IPC: H01L27/088
Filed: 1969-08-21
Abstract: 1282117 Infrared spectrometer HITACHI Ltd 21 Aug 1969 [6 Sept 1968] 41718/69 Heading G1A In an infrared spectrometer comprising at least one element plate having a large number of MOS elements thereon, means for cooling the element plate and means for directing infrared rays on to the element plate, an electrical circuit applies a different gate voltage to each element and the resulting radiation-induced channel currents from elements having adjacent gate voltages are subtracted, the difference currents being displayed serially and repeatedly on a cathode ray screen together with their corresponding gate voltages, thereby to present the intensity distribution of the infrared radiation. The element plate is cooled to such a low temperature that the MOS elements have sharp infrared absorption edges, the absorption edge wavelength of an element being dependent on the gate voltage applied to that element. Thus by measuring the difference between the respective channel currents produced when radiation falls on two elements having different gate voltages, a measure is obtained of the radiation intensity in the wavelength interval between the absorption edge wavelengths of the two elements. In the circuit of Fig. 3 each element is supplied with a different gate voltage from a potentiometer 20 and the current outputs from adjacent elements are subtracted by subtractors 24 (i), whose outputs are fed to AND gates 16 (i). Variable source-drain power supplies 23(i) maintain the photo-sensitivities of the elements mutually equal, thus compensating for the variation of photo-sensitivity with gate voltage. Pulses from a ring counter 41, driven by a clock pulse generator 42, are applied successively to the gates 16 (i)so that the difference currents are applied sequentially and repeatedly to an amplifier 46 and oscilloscope 44. The ring counter 41 also controls AND gates 21 (i)and thus the gate voltages are also displayed successively and repeatedly on the oscilloscope screen, simultaneously with their corresponding difference currents. In a further embodiment Fig. 2 (not shown), wherein the adjacent gate voltages are very close to one another, and channel current is hence virtually a continuous function of gate voltage, the differential of the channel current with respect to gate voltage is displayed on the oscilloscope against gate voltage. To increase the photo-sensitivity of the device groups of MOS elements, each group having the same gate voltage, may be employed. The different elements of each group may be distributed about the plate in such a way as to compensate for non-uniform illumination of the plate. To monitor continuously the radiation in a given spectral range, the AND gates 16(i), 21(i), OR gates 18, 22, CRO44, counter 41 and generator 42 are replaced by a change-over switch between the subtractor outputs and the amplifier 46, whose output is fed to a measuring and recording arrangement. In use, Fig. 4, the element plate 35 is mounted in an enclosure cooled by liquid helium. Radiation is directed on to the element by a mirror 30 and first passes through a filter 31. Specimen-holding recesses 32 and 33 are also provided. The spectrometer may be used to monitor the IR radiation from an explosion.