High voltage monolithic MOS driver arrays

This paper describes a unique self-scanned monolithic array of high voltage MOS transistors which control the piezoelectric stimulators in the Optacon tactile display developed at Stanford. This monolithic circuit performs both information processing (addressing and storage) and driving of 12 piezoelectric transducers. It contains a 12-bit dynamic shift register, a dynamic capacitor memory and 12 high voltage MOS driver transistors. The circuit has several unique requirements: 1. Low power operation (≈ 2mW). 2. Very low pn junction leakage (<10^-8A/cm²). 3. Dynamic information storage using 12 large (10pF) MOS capacitors. 4. High voltage operation (up to 60V) of the transducer driver transistors. 5. Minimum parasitic lateral pnp transistor action since substantial charge is periodically injected into the substrate by the driver transistors; this charge can interfere with shift register and memory operation. 6. Process compatibility with the low threshold voltage (-2.3V) P-channel self-scanned MOS image sensor of the Optacon. A technological procedure was developed to meet these requirements. Device properties were determined and charge injection and transport were measured. The circuit was fabricated in significant quantities (∼600 units) in the Stanford Integrated Circuits Laboratory with excellent yield ( > 50%). This high voltage transducer drive circuit represents a unique example of the interaction between system requirements and monolithic device technology in achieving optimum system design.