Measurements of leakage currents and the capacitance of the storage capacitor in a single DRAM cell

Methods of measuring leakage currents and the capacitance of the storage capacitor in a single DRAM cell have been developed for correlation with the electrode shape of the capacitor. In the circuit used for these measurements, the plate electrode of the storage capacitor is connected to the gate of the MOSFET which amplifies the voltage variations of the storage capacitor during the measurements. Here, only a conventional transistor parameter analyzer and a capacitance meter are required for the measurements. For the capacitance measurement, the linear region characteristics of the MOSFET are used to simplify the analysis. For the leakage current measurement, however, the subthreshold region characteristics of the MOSFET are used to enhance the accuracy of the measurement. The results show that the very low leakage currents (down to below 0.1 fA) and the capacitance (37.5 fF) of the storage capacitor can be measured accurately. Further, the leakage current-voltage characteristics of the storage capacitor are discussed by comparing with those of a large area planar capacitor whose structure is the same as the storage capacitor.>