Characterization of MODFET dynamic memory cells
Abstract
The MODFET structure was investigated to determine its suitability for dynamic memory applications. The MODFET DRAM capitalizes on the excellent speed and high charge densities at the MODFET heterointerface to yield a dynamic memory cell with good characteristics that is compatible with MODFET circuitry. The inversion charge layer present at the n-AlGaAs/GaAs heterointerface in equilibrium is used as the storage medium. The experimental approach involves characterizing both isolated MODFET capacitors and single-transistor cells to determine factors affecting charge storage in MODFET capacitors. Storage times were explored as a function of temperature, capacitor geometry, and fabrication technique. The capacitance recovery transient of the storage capacitor was used to isolate and characterize leakage mechanisms. Charge transfer from the DRAM cell was studied with the use of an analytical model, and a numerical model. Writing to and reading from the DRAM cell were characterized. In an isolated capacitor, storage times of 4.3 hours were observed. In the DRAM cell, storage times exceeding 200 s are presented. Cell operation was demonstrated for 25x25 $\mu$m capacitors, with access time of less than 10 ns.
Degree
Ph.D.
Advisors
Cooper, Purdue University.
Subject Area
Electrical engineering
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