Fabrication and operation of CCD structure with silicon layers grown on sapphire substrates

Two CCD's, one 2 bits long and one 64 bits long, were fabricated from silicon on sapphire wafers. The 2-bit device is a resistive gate structure which can be operated ten times faster (2 MHz) than the normal structure of the same size. The reason is found to be due to the special structure of the resistive gate structure. The 64-bit device is processed on bulk silicon so that a direct comparison can be made. Both SOS and bulk silicon can be operated at 20 MHz or higher. At high-frequency operation, both devices have about the same transfer efficiency. But at the low-frequency end, the SOS device shows the dark current to be very high with the device barely operating at 600 KHz.