A monolithic lead sulfide-silicon MOS integrated-circuit structure

A process for directly integrating infrared photoconductive lead sulfide (PbS) detector material with metal-oxide-semiconductor (MOS) transistors has been developed. The processing technology is based on the conventional PMOS and CMOS technologies with a variation in the metallization. Instead of aluminum, a layer of chromium is deposited followed by a gold deposition. This modification is required to ensure device survival during the chemical deposition of the PbS. A variety of structures based on an implanted PMOS process were fabricated and evaluated. In the interest of simplicity, one of the basic structures that was evaluated was one where the PbS is directly coupled to the gate of a PMOS. External bias, load, and source resistors are connected and the circuit is operated as a source-follower amplifier. Radiometric evaluations were performed on a variety of different geometry metal-oxide-semiconductor field-effect transistors (MOSFET´s). In addition, an array of detector elements was simultaneously fabricated to demonstrate small element capability. Elements of 25 × 25 µm were easily fabricated. Room temperature evaluation using a filtered 700-K blackbody source yielded a D* (at peak wavelength) of 10¹¹cm Hz^1/2/W at 100-Hz chopping frequency.