Considerations for CPM measurements of fast switching ionizers

Charged Plate Monitors (CPM) are commonly used to calibrate and monitor ionizer performance. When the CPM was developed, it did an excellent job of characterizing ionizer performance for an ionizer used in a 150 mm wafer fab as well as many other applications, including DC applications. Today, there are a number of ionizers operating at higher frequencies, including pulsed AC and piezoelectric ionizers. In these cases, the underlying physics is in a new regime and conventional measurements do not exactly apply. Details of the CPM wave shape and the application must be considered when using such ionizers. These effects need to be accounted for in standards that apply to CPM use, when measuring ionizer performance.