Apr 20th, 1:00 PM - 4:00 PM


Initial Investigations of Sub-RF AC Methods for Metal-Oxide- Semiconductor Devices and Trap-Based Flash Nonvolatile Memory

Faculty Sponsor

Dr. Bill Knowlton and Dr. Bernard Yurke


Presently, nearly 109 metal-oxide-semiconductorfield- effect-transistors (MOSFETs) are used in a single computer microprocessor or memory chip. A MOSFET is comprised of a conductor, semiconductor and nonconductor or insulator materials in a layered configuration consisting of metal-SiO2-Si. High dielectric constant (k) insulators, such as HfO2, are being used as alternatives to the traditional SiO2 insulating layer. The number of MOSFETs in microprocessors and memory continue to rise, but the microprocessor and memory chip size essentially remains constant. Hence, MOSFET dimensions are continuously downscaled and the thickness of SiO2 has decreased to less than 10 monolayers which severely degrades its insulative properties. As the number of charged carriers (i.e., electrons) increases through the thin SiO2, the leakage current (electrons/second) increases rapidly and power consumption and heat increases by the square of the current. Because of their dielectric properties, thicker high k insulators can replace the thinner SiO2 thereby decreasing the leakage current and power consumption without compromising MOSFET performance. However, a thorough investigation of high k insulators in MOS devices is in need. This work seeks to investigate high k insulators via two areas of investigation. The first involves the investigation of several sub-radio frequency (RF) alternating current (AC) methods to examine carrier transport mechanisms in HfO2. The sub-RF AC methods include using impedance methods and a lock-in amplifier to examine the AC conductance in dielectric layers. The second area of investigation involves a new area of MOS non-volatile memory (NVM) called charge trap-based flash (TBF) memory. Currently, the NVM that is used has a layered configuration consisting of metal-SiO2-Si-SiO2-Si. As the SiO2 thickness decreases and leakage current increases, alternative layered configurations that incorporate high k insulators are required. In collaboration with Oregon State University and Penn State University, metal- Al2O3-Ta2O5-Al2O3-Si devices will be examined and characterized as a potential NVM replacement.