Picosecond photoconductivity in low-temperature-grown GaAs (LT GaAs) has been used to provide temporal resolution both in rigid probes and in scanning force microscope probes. This article reviews the fabrication and use of such probes. 2.5 ps temporal resolution and few microvolts sensitivity are obtained at arbitrary points on circuits with a spatial definition of 100 nm. Rigid probes are tested in application to analogue and digital circuits. As an alternative to electron beam testing, scanning force probes are applied to in situ imaging and waveform measurement. Finally, the use of time-resolved waveform analysis with scanning-force microscopy probes with semiconductor laser sources is demonstrated.
New discoveries in fabrication technology and in device physics have open the way for a class of electronic and optoelectronic devices with nanometer-scale dimensions. These devices offer the opportunity to work with electrons confined to 2-D, 1-D and 0-D in space. In an effort to understand how individual devices work it will be necessary to interrogate individual submicron structures. Aside from the fine dimensions of the contacts used for such measurements it will be necessary to make measurement with very low invasiveness and increasingly, with higher speed. To meet the challenges of new nano-technologies we have developed a probe which demonstrates high impedance voltage measurement using a 0.1-micron contacting tip. The voltage of the tip is photoconductively sampled allowing waveforms to be measured with picosecond resolution [1]. In this paper we describe the operation of the probe using a gain switched laser diode to make measurements which extract only a few fC from the device under test. We also show the probes value as a high-speed, high sensitivity probe for millimeter-wave circuits.
We have developed an optical delay tester based on electro-optic sampling, and designed a prototype to test the timing of high-speed IC chips. The device puts an electro-optic crystal in contact with the terminals to be tested and measures the voltage waveform applied to the crystal. Measurement precision is 100 mV or better and timing precision measurement is 50 PS.
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