Principal Investigator Harry Tuller
Co-investigator Geoffrey Beach
High-k dielectrics play a key role in modern microelec- tronic circuitry, given their ability to provide reduced leakage currents while providing adequate capacitance in ever smaller nano-dimensioned metal-oxide semiconductor field-effect transistor (MOSFET) devices. Recently, the Beach group at MIT demonstrated the ability to modulate the magnetic properties of transition metal thin-films by electrical bias across thin-films of Gd2O3. The reversible switching was demonstrated to be assisted by the electro-migration of oxygen ions to and away from the transition metal/Gd2O3 interface. This novel process, now called “magneto-ionic control,” creates new opportunities for nonvolatile information storage.
Like magneto-ionic device, there is another important emerging device called “memristor” which applies field driven ionic transport-controlled property toggling. Though this device has been researched widely for a decade and defect chemistry of dielectrics is critical to the device operation, understanding of defect chemistry of dielectrics used for memristors are still limited. Here, we have examined electrical and transport properties of Gd2O3 via impedance spectra as a function of temperature and oxygen partial pressure considering Gd2O3 as a model oxide for ionic migration- controlled devices. In this research, we found that Gd2O3 can be electronic or mixed ionic-electronic conductor at high-temperature via controlling doping and phase. This research will be continued to the lower temperature regime to understand the correlation between the behavior of such devices and defect chemistry of dielectrics.
In addition, we have begun an investigation of the mechanism of magneto-ionic devices in a viewpoint of considering magneto-ionic device as an electrochemical cell. Previous research indicated that this device behaves in a manner similar to high- temperature electrochemical devices. We are preparing model devices that reflect features of both magneto- ionic and electrochemical devices and are examining their properties in situ.