Charge-Trap Transistors for CMOS-Only Analog Memory

Since our demonstration of unsupervised learning using the CMOS-only charge-trap transistors (CTTs) as analog synapses, there has been an increasing interest in exploiting the device for various other neural network (NN) applications. However, most of these studies are limited to mere simulation due to the absence of detailed experimental device characterization. In this article, we provide a comprehensive investigation of the programming behavior of CTTs, including analog retention, intra-and inter-device variation, and fine-tuning of the device, both for individual devices and for devices in an integrated array. It is found that, after programming, the channel current gradually increases to a higher level, and the shift is larger when the device is programmed to a higher threshold voltage. With this postprogramming current increase appropriately accounted for, individual devices can be programmed to an equivalent precision of five bits, and three bits can be achieved for devices in an array. Our results reveal the promising future of using the CTT as a CMOS-only analog memory device.