Ph.D Thesis

Ph.D StudentYalon Eilam
SubjectNovel Bipolar Transistor Structures and their Applications
DepartmentDepartment of Electrical and Computer Engineering
Supervisor PROF. Dan Ritter
Full Thesis textFull thesis text - English Version


This thesis presents several new bipolar transistor structure based upon compound semiconductors and their applications. The main structure studied is a metal insulator semiconductor bipolar transistor, the insulator layer being a resistive memory film. We show that this device provides useful information on the conduction, temperature, and switching effects in thin films. The device separates the electrons injected into the conduction band from those injected into the valence band of the semiconductor electrode. The main application of the device is the study of new materials for non-volatile memory technology.

Conventional non-volatile memory technology is approaching its scaling limits, and the development of alternative devices has become crucial. Resistive switching random access memory (RRAM) is among the leading future non-volatile memory technologies; however, its implementation is hampered by the lack of full understanding of the switching and conduction mechanism as well as the lack of detailed physical models.  The resistive switching effect is attributed to the formation and rupture of conductive filaments in metal oxides. Most studies of the switching phenomena are carried out using 2-terminal metal-insulator-metal structures. Here we use the 3-terminal device in order to provide additional information, not available using just two terminal devices.

First, we demonstrate how the local filament temperature is determined on a nano-metric scale by analyzing the thermal excitation rate of electrons from the filament Fermi level into the conduction band of a p-type semiconductor electrode. This information is crucial, since the local temperature plays a key role in the switching effect. Next, we discuss the various possible heat dissipation mechanisms in light of the experimental results, and compare thermal simulations to the measured temperatures. The main conclusions obtained are that filament tip diameter is of the order of few nano-meters, and that the thermal resistance of interfaces plays a major role in determining the filament temperature. Finally we study the filament growth dynamics. The device was used to experimentally determine the filament growth direction under varying conditions and validate our model of filament formation. The model shows that the growth direction is determined by the relation between electrode and bulk oxide kinetics.