Light-to-Dark Current Ratio Enhancement on MIS Tunnel Diode Ambient Light Sensor by Oxide Local Thinning Mechanism and Near Power-Free Neighboring Gate

A charge coupled metal insulator semiconductor (MIS) tunnel transistor after self-protective oxide breakdown process was used for ambient light sensing. The drain part of the transistor is an MIS tunnel diode (TD) with ultrathin oxide, which collects the light and dark currents. A surrounding MIS gate with thicker oxide is placed beside the drain at a distance smaller than 1 μm by the method of controlling the undercut of wet etching. Under illumination, the transfer curve of the transistor shows a low subthreshold swing smaller than 60 mV/decade due to the aid of photoemission to the double-exponential mechanism controlled subthreshold current. The device after drain breakdown process shows significant enhancement of light-to-dark current ratio comparing to either single MIS TD or the same structure without breakdown. Also, no additional power is included with the added gate voltage because of the low leakage gate structure. Comparing to the case without gate voltage, the maximum light-to-dark current ratio at a suitable gate voltage shows lower power dissipation, which meets the need of low-power requirement in nowadays' electronic devices.