Sensors: A New Class of Devices Based on Interfacial Effects in Metal-Semiconductor Hybrid Structures

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1. Intellectual MeritWe have recently demonstrated experimentally that hybrid thin film structures possessingan appropriately selected geometric interface between a semiconductor and a metal display anew phenomenon that has been labeled extraordinary magnetoresistance (EMR) and that InSbdevices with either internal or external Au shunts exhibit room-temperature EMR as high as100% to 750,000% at magnetic fields, ranging from 0.05T to 4 Tesla, respectively. Thesenonmagnetic structures are readily fabricated for practical sensor applications such as read-headsfor ultra-high density magnetic recording and rival the performance of conventional sensorsbased on the giant magnetoresistance (GMR) effect. We have also demonstrated that EMRdevices are scalable from macroscopic to nanoscopic dimensions in the range of millimeters to20 nanometers. It has recently been realized that EMR is but one example of a broad class ofgeometry-driven interfacial effects in hybrid semiconductor-metal structures. Now a secondexample of such interfacial phenomena, extraordinary piezoconductivity (EPC), has also beendemonstrated by Solin et. al. Here we propose to establish proof of principle, elucidate theunderlying physics and develop prototypes of a new class of ifEXXly sensors in which thesensitivity of the metal-semiconductor interface to external perturbations gives rise to similarextraordinary responses. In the case of EMR we propose new prototype array structures forultra-high resolution magnetic sensing and magnetic imaging. For EPC we propose to clarify thephysical principles and to develop prototypes of ultra sensitive and robust strain and pressuresensors. For extraordinary electroconductance (EEC), extraordinary thermoconductance (ETC)and extraordinary optoconductance (EOC) devices we will first establish proof of principal andthereafter move to the prototype stage.All EXX effects are critically dependent on the geometry and physical properties themetal-semiconductor interface. We have already shown that the finite element method (FEM)for modeling EMR provides excellent ixno adjustable parameterl" agreement with experimentswhile revealing the current and potential distribution in the device in exquisite detail. Therefore,we propose collateral investigation of these novel EXX effects using FEM modeling since itincorporates geometrical issues, while accounting for the attendant complex boundaryconditions. FEM is also ideally suited for the design optimization of the structures in order toenhance sensitivity.2. Broader ImpactIt is anticipated that the proposed research will have broad beneficial impact oneducation, technology, and society. It will expose graduate and undergraduate students from anumber of disciplines/departments to new experimental techniques, basic physical principles,and novel fabrication methods related to EXX sensor development thus providinginterdisciplinary skills that will be mandatory for the next generation of the nation's scientistsand engineers. Research results will also be integrated into the undergraduate course work atboth institutions and into a special topics course for ioMagnetlo high school students. Theproposed research will enhance the opportunity for adding women and under-representedminorities to the Washington University faculty through hiring programs currently chaired by thePI. It will also significantly augment the development of a new campus-wide MaterialsInitiative/Center that is lead by the PI. EXX sensors could impact a variety of diversetechnologies including sensors for medical applications, manufacturing quality control,automobile safety, pollution-control and fuel-efficiency, thermal imaging devices and consumerelectronics with obvious social, medical and economic benefits.