UNIVERSITY OF UTAH
ELECTRICAL AND COMPUTER ENGINEERING DEPARTMENT
THESIS DEFENSE FOR THE DEGREE OF
MASTER OF SCIENCE
Nurunnahar Islam Mou
Advisor: Massood Tabib-Azar
Experimental and simulation study of gate controlled resistive switching memories
Scaling limitation of current memory technology requires invention of new class of memory that has high density, fast programming and access time as well as good non-volatility. Memristors are good candidates for such application and researchers are investigating memristors vigorously now-a-days. Anticipated advantages of these devices are long retention time, high access speed, endurance, low power and high density. Memristors were first proposed theoretically as the fourth circuit element by L. Chua in 1971 but it did not came into practical implementation until 2008 when researchers in HP lab fabricated and recognized the first ever memristor. However, the research on memristor dates back to 1964.
There are several significant contributions within the scope of this research work. This thesis work demonstrates the fabrication and operation principle of gate controlled resistive switching memory device. The fabricated gated memristors are among first of its kind. In-depth studies of the switching layers used in the fabricated gated memristors are also presented prior to the fabrication process. Firstly, two switching layers i. e. Cu2S and Ag2S are selected to be used in our devices. Using advanced characterization techniques such as Atomic Force Microscopy, growth of metallic conductive filaments are observed under voltage magnitude and polarity. Secondly, larger two terminal memristor (Au/Ag2-xS/W) was fabricated to study the time dependent switching behavior of Cu2S and Ag2S layers. This study was further extended to demonstrate the effects of illumination on the switching kinetics of the fabricated devices and it was found that the average switching time of these devices got significantly decreased under illumination.
Third, a novel three terminal gated memristor was proposed and fabricated. The motivation for this work arises from the fact that we would like to tune the switching voltage of the memristors so that they can be used as sensors and/or integrated switches in non-volatile memory. The new recessed gate electrode introduced in this structure was able to guide the charged metallic ions depending on how much voltage was applied at the gate and either aid or inhibit the formation of the conductive filament. As a result, different turn-off voltage was observed for different gate voltages. These devices also exhibit very high sub-threshold slope which make them suitable as low power switches.
Last but not the least; a numerical simulation model was developed to explain the gate electric field effect observed in our fabricated Pt/Cu2-xS/Pt based gated memristor. Through the simulation it was shown that, application of gate voltage results in bending and narrowing of the conductive metallic filament. The bending is away or towards the gate structure depending on the polarity of the gate voltage applied.
Friday January 29, 2016
Sorenson Molecular Bioengineering Building (SMBB) Room 3750
The public is invited