RESONANT TUNNELING DIODE FOR STATIC RANDOM ACCESS MEMORY CELL APPLICATIONS

Abstract

In this thesis the double barrier resonant tunneling diode (DBRTD) and its applications in the static random access memory (SRAM) cell circuit have been studied. A simplified analytical model has been developed to calculate the I-V curves of DBRTDs. Based on the calculated results, it has been shown that a thinner barrier and a larger barrier height produce a larger peak to valley current ratio (PVR), and a thinner well width and heavily doped electrodes provide a larger tunneling current. A DBRTD epi-layer structure based on the GaAs/AlAs materials system has also been designed. Negative differential resistance of fabricated DBRTDs was observed at room temperature, the highest peak current density measured was 0.59 x 104 A/cm2 and the peak to valley current ratio (PVR) was 2 - 2.3. A new SRAM cell circuit based on DBRTDs has been proposed and designed, with two DBRTDs connected in series lo achieve the bistable and memory behavior, and a third DBRTD to access the input/output node. The SRAM cell circuit has been successfully fabricated using the GaAs/AlAs material system. Measured DC characteristics have confirmed the memory characteristic of the SRAM cell. In addition, the selective read and write operations of the SRAM cell, which are significantly different from those of the conventional six-transistor SRAM cells based on MOS technologies, have been confirmed by SPICE simulation. A very simple piece wise linear (PWL) approximation was used to represent the DBRTD in the simulation. Suggestions on the reduction of static power consumption and the improvement of the transfer characteristics of the SRAM cell have been presented.