Analysis and measurement of a photo diode used as a control gate in a floating-gate MOS transistor

This paper reports a new operating use regarding the floating-gate MOS transistor (FGMOS). Here it is demonstrated that the typical open circuit voltage (VOC) of a CMOS integrated photo sensor can be coupled to the floating gate of a FGMOS. Several photo sensors structure designs are studied and measured. Results demonstrated that the threshold voltage of the transistor can be modulated optically with a series array of photo sensors to increase the coupled voltage. Therefore, a micro solar cell integrated with a CMOS technology can be used as a control gate giving an optical alternative to modulate the I-V characteristics of a FGMOS, extending the reliability of this device beyond the known injection phenomena commonly used to program it. Also, more than one control gate can be used with only one transistor, giving opportunity to explore the convenience to use this proposal within a pixel design since only one transistor is used, with its floating gate as a summing node.