ELECTRICAL CHARACTERIZATION OF METAL - ZINC OXIDE - SILICON DIOXIDE - SILICON STRUCTURES
Abstract
Two of the basic problems associated with monolithic Metal - Zinc Oxide - Silicon Dioxide - Silicon (MZOS) surface acoustic wave devices involve (1) drifting of device characteristics due to charge injection and trapping associated with the ZnO and (2) radiation damage in the Si-SiO(,2) subsystem. Both of these problems are addressed in this thesis. A quantitative comparison of radiation damage occurring during rf magnetron and rf diode ZnO sputter depositions is first performed. Regardless of the deposition technique, mid-gap D(,it) values in as-deposited samples are typically observed to be in the low to mid 10('11) states/eV-cm('2) range. Flatband shifts range between (+OR-)1 to -6 volts (for a 1000 (ANGSTROM) thick SiO(,2) layer), with both D(,it) and (DELTA)V(,FB) being spacially dependent. By incorporating a low temperature post-deposition (PZ) anneal into the fabrication procedure, it is shown that a significant improvement can be made in the characteristics of the Si-SiO(,2) subsystem. Complete removal of the damage, however, is only observed to be possible through the use of techniques which are incompatible with standard MZOS deposition procedures. The low temperature post-deposition anneal is next exhibited to have a significant effect on the stability of magnetron-sputtered MZOS devices. Utilizing temperatures in the 380(DEGREES)C - 490(DEGREES)C range, it is shown that complete removal of the troubling bias instability can be achieved. Based upon measurements which reveal similar ZnO-SiO(,2) interface properties in diode and magnetron structures, the bias-stable characteristics observed in magnetron devices are concluded to arise from a difference in the bulk properties of the two types of ZnO films. To identify the mechanism responsible for the aforementioned stability, diode and magnetron sputtered devices are subsequently examined using small signal admittance measurements. It is concluded that electrically active bulk traps are present in much larger densities in magnetron films than in diode films. A model linking the existence of these traps and the achievement of stability is presented.
Degree
Ph.D.
Subject Area
Electrical engineering
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