Control of subthreshold characteristics of narrow-channel silicon-on-insulator n-type metal-oxide-semiconductor transistor with additional side gate electrodes

A silicon-on-insulator (SOI) n-type metal-oxide-semiconductor (MOS) transistor with additional side gate electrodes is fabricated and its subthreshold characteristic. are discussed. Since its device structure provides independent biasing to gates, flexible device-characteristic control for the respective device is expected. The key fabrication process is the formation of transistor gates. Additional side gate electrodes are formed by reactive ion etching (RIE) with a SiO2-covered top gate as an etching mask. Subthreshold characteristics are improved by negative side-gate biasing. In addition, the side-gate voltage V-SG required to decrease off-leakage current by one decade is around 100 mV. Since the sidewall oxide thickness is chosen to be 5 nm, which is the same as the top-oxide thickness, rather sensitive subthreshold-characteristic control compared with that of biasing through a thick buried-oxide layer is achieved in response to performance requirement. In the viewpoint of stand-by-power suppression, these provide a certain controllability to a circuit operation.