Picoseconds measurement of internal waveforms in integrated circuits using sampling force probing. II. Applications, capabilities, and limitations

As integrated circuit density and speed increase their testing becomes crucial to the design cycle as well as a difficult task. To provide proper circuit diagnostics, an adequate test instrument must be capable of providing noncontact measurement at internal points in integrated circuits with high spatial and temporal resolution. Techniques based on noncontact pulse sampling electrostatic force microscopy are proving to be successful candidates for the internal testing of high frequency integrated circuits. In these techniques, internal circuit voltages are determined by sensing the local electrostatic force on a miniature probe that is closely positioned above the circuit test point. Recently, a pulse sampling technique that utilizes a pulse width modulation method has been proposed to enhance the temporal resolution of the force microscope instrument. Only a proof of concept of the pulse width modulation method has been presented. This paper demonstrates the capabilities of the method to measure high frequency signals and provides an analysis in terms of its sensitivity and time resolution. Measurement of a 500 Mbit/s clock signal is presented with a temporal resolution of 50 ps. The technique can provide measurements with voltage sensitivity down to 10 mV_rms/√Hz