Modelling of electrical charge injection into charge-coupled devices

Abstract

A detailed study of signal‐charge injection into surface channel CCDs as a response to a gate‐voltage step is carried out. The analysis is based on the time‐dependent diffusion equation with the fringing field term included. With the appropriate boundary conditions, this equation is applied to the input diffusion, input gate, and succeeding gate of a CCD. It is found that injection of signal charge into the device is characterized by three distinct processes. First is the transient time required by the input diffusion to establish a constant injection current under the input gate, then, the input stage enters into a constant current injection mode, and finally when the surface potentials of the input and receiving gates equilize, the injection current decays to zero. An analytical expression for the transient component, and for the total time required to inject a packet of charge into the CCD is derived. Experimental results obtained on a CCD agree well with the theoretical predictions.