A high-current IrO/sub x/ thin-film neuromuscular microstimulator

Abstract

The authors report the development of a high-current stimulating electrode and a versatile fabrication technology required for the eventual realization of an implantable microstimulator for neuromuscular applications. The stimulating electrode is based on thin films of activated iridium oxide (AIROF), and is formed by combining more than 450, 20 mu m*20 mu m, small AIROF sites. It occupies a total active area of approximately=180000 mu m/sup 2/ and has been subjected to more than 350 million charge-balanced constant current pulses of 10 mA amplitude and 200- mu s duration without showing any sign of degradation. A versatile fabrication technology has been developed which offers high-performance CMOS and bipolar devices, together with Zener diodes, on-chip poly-Si/poly-Si capacitors, and high-value resistors. Isolated vertical npn transistors with current gains of 140-150, lateral pnp transistors with current gains of 10-20, and 7-V voltage references are available and have been used to implement an integrated circuit chip for an implantable neuromuscular microstimulator. The chip includes 3.5-V and 8-V regulators, RC low-pass and high-pass filters, and regulated current sources and sinks, and measures 1.9*1.2 mm/sup 2/.