Design and fabrication of a charge-coupled device

Abstract

The structure and the operation of a Charge-Coupled Device (CCD) have been studied and a p-channel, 16 bit ConductivelyConnected CCD has been designed and fabricated. The device has surface channel structure, where the holes which are the minority carriers representing the signal voltage are stored at the Si surface and transferred along it. The operation of the device is in 1$\frac{1}{2}$ phase mode, hence a clock pulse is applied to the phase 1 electrodes and phase 2 electrodes are held fixed by a dc voltage. The device consists of a source diffusion which forms an input structure together with two input gates, and 32 transfer gates followed by an output gate and a drain diffusion. The CCD channel was confined by the thin oxide and no channel stop diffusion has been made. Niche mode has been adopted as an input scheme because of its linear and low noise characteristics, and the independency of the threshold voltages of the input gates. The first input gate is dc biased and input signal voltage is directly applied to the second input gate with sampling pulse applied to the source diffusion. The asymmetry in potential profile necessary for the charge flow is obtained by ion implantation. Non-destructive output is obtained by sensing the surface potential under phase 2 electrodes with sensing diffusions. The gate of the output MOS transistor senses the potential variation of the sensing diffusion and output results at the source of the output MOS transistor. The device has 8 bit tapped outputs, thus it can be used to convert the serial input to parallel output or as a variable delay line. The results obtained from the test patterns and the characteristics of CCD have been analyzed and discussed.