A Microwave-Bandwidth Waveform Monitor for Charged-Device Model Simulators.

The Charged Device Model (CDM) describes a form of Electrostatic Discharge (ESD) that is a growing hazard in the microelectronics industry as factories become more automated. A CDM event occurs when a device gets charged by friction, then discharges by touching a grounded surface. To verify the ability of semiconductor devices to withstand the CDM threat, they must be tested with CDM simulators. Although there are no commercially available CDM simulators, many organizations have made their own using published designs. We found that the monitor output of one widely used CDM simulator deviated substantially from the actual current flowing from the charged device because of parasitic inductance in the monitor circuit. We devised a new CDM waveform monitor based on microwave technology, using components whose geometrical symmetry guarantees that the monitor will be free of parasitic reactances when handling CDM waveform frequency components above 1 GHz. The apparatus uses readily available components and is extremely simple to make. In addition, we have developed a procedure to measure our monitor's frequency response with a microwave network analyzer, confirming that its bandwidth is at least 4 GHz. This frequency domain method extends the ability to measure the impulse response of the probe well beyond the bandwidth available with common oscilloscope methods. The new waveform probe will provide the ESD community with the ability to evaluate competing CDM simulators when they become commercially available and to correlate the results of semiconductor device tests.