DRAM Cell Characterization by AC-Impedance Measurement

A novel characterization technique for DRAM test cell arrays is presented. The new method permits the extraction of subthreshold IV-characteristics of the cell transistor and its threshold voltage with no DC contacts to the source. The DRAM cell is viewed as an equivalent circuit of resistors and capacitors, whose values can be determined by sweeping the frequency of the AC-impedance bridge. Using this technique, it is possible to characterize the cell transistor in its natural habitat without resorting to special test structures.