Floating-gate devices: they are not just for digital memories any more

Since the first reported floating-gate structure in 1967, floating-gate transistors have been used widely to store digital information for long periods in structures such as EPROMs and EEPROMs. Recently floating-gate devices have found applications as analog memories, analog and digital circuit elements, and adaptive processing elements. Floating-gate devices have found commerical applications, e.g. ISD, for long-term non-volatile information storage devices for analog applications. The focus of floating-gate devices has been towards fabrication in standard CMOS processes, as opposed to the specialized processes for fabricating digital non-volatile memories. Floating-gate circuits can be designed at any or all of three levels: analog memory elements, capacitive-based circuit elements, and adaptive circuit elements.