NaNO2thin films for pyroelectric detector arrays

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Abstract
Integrated NaNO2 pyroelectric radiation detectors have been made by growing NaNO2-films from the melt directly on silicon. The pyroelectric signal is read out by an integrated circuit in the Si-substrate. The detectors, single element or arrays, can be coupled to the electronics in two ways, either by the ferroelectric field effect at the NaNO2-Si contact, or by separate MOS-FETs. The performance of the electrical coupling by the ferroelectric field effect is strongly limited by the trapping of charge in interface states. The performance of signal transfer to a MOS-FET is more efficient, but suffers from a large capacitive load, if the gate of the MOS-FET is connected to the lower detector electrode formed by metallization on the silicon chip. Impedance matching therefore requires a small thickness of the NaNO2-film. A small thickness, on the other hand, favors the penetration of the temperature wave into the substrate with the accompanying heat loss. Electrical and thermal optimization are thus contradictory. A solution could be to remove part of the silicon underneath the detector area.