A 7.8V neurostimulator based on cascoded low-voltage Silicon-on-Sapphire MOS transistors

Sapphire has better biocompatibility than silicon, higher mechanical resistance (second only to diamond), it is transparent to wavelengths ranging from 150 nm (UV) and 5500 nm (IR), and its lattice matches very well to Si and GaAs. Those unique characteristics enables Silicon-on Sapphire (SoS) technology as a potential solution for implementation of implantable electronic devices, such as retinal prostheses, combining optics, mechanical support and electronic devices. However, some issues are yet to be solved, such as high cost, and voltage supply limitations. Designing “high-voltage” (HV) tolerant circuits using standard low-voltage transistors is a more cost-effective solution for avoiding expensive process modifications. This paper presents circuit topologies and simulated results from a neural stimulator rated for 7.8V supply using standard low-voltage transistors in Silanna Silicon-on-Sapphire 0.5μm/FC process. The implemented stimulator consists of a classic current-steering digital-to-analog converter (DAC), four “high-voltage” switches constituting a stimulator bridge, and clock-shifters, for controlling the switches.