Semiconductor image sensor and the method of operating the same

Abstract

A semiconductor image sensor of wide dynamic range, high sensitivity, low noise and high image clarity, which is provided with a hook structure for detecting radiant energy input information, a readout transistor and means for refreshing stored optical information and which is capable of non-destructive readout of optical information, and a method of operating such a semiconductor image sensor. The impurity concentrations in the hook structure, their distribution profiles, materials of layers forming the hook structure and their thicknesses are so selected as to optimize the carrier storage function of the hook structure, thereby permitting the non-destructive readout of the optical information. The ratio between the junction capacitance and the earth capacitance of a floating pn junction establishing a potential barrier in the hook structure is selected so that a stored voltage in the floating pn junction and the readout sensitivity may become maximum. By repeating the non-destructive readout, as integrated value of the quantity of incident light is read out. The time interval to a first operation of the readout transistor after the operation of a refresh pulse signal is selected in accordance with the quantity of the incident light, by which an electric signal proportional to the quantity of the incident light can be read out. The refresh operation is performed by applying a pulse voltage in such a manner that a bias voltage may be provided to a substrate electrode or surface electrode in a light integration period alone and, in the refresh period, the pulse voltage is made zero or negative.