Tunneling Transistor And Its Application In Memory

With the development of the Ultra-Large Scale Integrated circuits technology, the number of devices integrated into one single chip is becoming larger. This renders the technology node to be scaled down, thus, the leakage current will grow up. This trends has brought high power consumption problems, to overcome this challenge, one solution is to reduce the subthreshold swing value and the leakage current. The tunneling field-effect-transistor (TFET) has low subthreshold value and low leakage current, however, its drive current is several decades smaller than that of MOSFET, thus it has limited applications in logic fields. But in this paper, we look into its special applications in memory fields, which makes this shortage less critical. First, a novel channel recessed TFET (UTFET) is designed and investigated, simulation results show that it has a boosted drive current and a suppressed leakage current. And then a novel floating-junction-gate dynamic random access memory (FJG-DRAM) is designed and investigated.For the UTFET, since the channel is recessed into the substrate, it has a enlarged line tunneling area without additional size increase, thus the drive current is enhanced, at the same time, the leakage current is suppressed due to the actually longer channel length.The FJG-DRAM is a combined device. It consists of one floating gate MOSFET and one gated diode. The gated diode is the write unit, and the MOSFET is the access unit. When the gated diode is forward biased, there is a large current flowing through it, and state "0" can be written into the floating gate. When the gated diode is reversely biased, it works as a p-type TFET, thus there is a band-to-band tunneling current flowing through the pn junction. Then, state "1" is written into floating gate. This device has the advantages of fast write speed, reduced cell size, good disturb and retention performance. Most importantly, its fabricating processes are compatible with that of flash memories, thus it can be used as embedded DRAMs on SoCs.