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

Since the rst reported oating-gate structure in 1967, oatinggate transistors have been used widely to store digital information for long periods in structures such as EPROMs and EEPROMs. Recently, oating-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 oating-gate devices has been towards fabrication in standard CMOS processes, as opposed to the specialized processes for fabricating digital nonvolatile 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. In 1967, Kahng and Sze reported the rst oating-gate structure as a mechanism for nonvolatile information storage [1]. Since then, oating-gate transistors have been used widely to store digital information for long periods in structures such as EPROMs, EEPROMs, and Flash memories [2, 3]. Figure 1 sketches the growth of non-volatile digital technology from the inception of the oating-gate device in 1967. These digital nonvolatile memory technologies have only been fabricated on specialized IC processes. Even though digital memories have been the primary application for oating-gate devices, recently oating-gate devices have been used as circuit elements. Floating-gate devices are not inherently digital memories, it only depends upon the way the circuit designer uses the available technology. Figure 1 also sketches the progress of oating-gate devices and circuits other than EEPROM devices. The research in oating-gate circuits has been exponentially increasing over the last several years; the goal is to further develop this technology to give researchers a wider set of solutions in solving integrated circuit problems. The focus of this paper, which introduces the special session on oating-gate devices and circuits, is to show that oatinggate devices are not just for memories anymore, but are circuit elements with analog memory and important timedomain dynamics. Georgia Institute of Technology, Atlanta, GA 30332-0250, e-mail: [email protected] Cornell University, Ithaca, NY 14853-5401, e-mail: [email protected] University of Washington, Seattle, WA 98195-2350, e-mail: [email protected] Kahng and Sze (?) FG Devices and Circuits log 1989 1999 ETANN Brooke, et.al