On-wafer analog pulse generator for fast characterization and parametric test of resistive switching memories

The development of new generation nonvolatile memories, such as Phase Change Memories (PCMs) and Resistive-RAMs (ReRAMs), calls for accurate and controllable programming pulses, which are fundamental to adequately characterise the memory cell. Indeed, the final cell state depends on parameters of the applied programming pulse(s), such as amplitude, duration, and fall time. The performance and the flexibility of conventional automated test equipment (ATE) should be enhanced to carry out reliable tests on different cell implementations, which may have different architectures or material compositions. Aiming at this goal, we designed, fabricated, and experimentally evaluated an on-wafer pulse generator, controlled by commercial ATE, which is able to provide voltage pulses with programmable amplitude, duration, and fall time. A key design requirement was to allocate the generator in the wafer scribe lanes, to reduce the impact of the proposed approach on testing cost. However, this requirement implies that the system must feature reduced silicon area occupation and have a very disadvantageous aspect ratio as well as limited pad count. Since unavoidable process spreads and nonidealities can affect the accuracy of the on-wafer pulse generator, a calibration procedure for pulse parameters was conceived, implemented, and validated. The designed system is able to generate pulses with an amplitude from 0.5 V up to 4.5 V, a pulse duration from 50 ns to 350 ns, and a fall time from 10 ns to several μs (the variability of the last parameter is essential to analyze the response of PCM cells to different quenching times). By using the proposed calibration procedure, it is possible to obtain an accuracy better than ±10% in all the parameters that define the shape of the generated programming pulse. Measurements on a fabricated prototype showed the effectiveness of the presented approach.