Micromachined photoconductive near-field probe for picosecond electric-pulse propagation measurement

Abstract

Electrical engineering has been progressing at an unexpected rate. Especially, the increase of operating frequency is one of the most desirable and explicit trends. However, this frequency increase has driven many field-related high-frequency electric phenomena into real consideration. As an effort to overcome the limit of conventional test instruments in diagnosing the high-frequency phenomena, optical/optoelectronic techniques such as photoconductive (PC) sampling and electro-optic sampling using a short pulse laser introduced, have opened new era for the characterization of ultrahigh frequency electromagnetic phenomena in the time-domain. Especially, the PC sampling technique has become one of the most promising test methods for the time-domain electric phenomena characterization, due to the ultrawide measurement bandwidth extending to multi-hundreds gigahertz and the very high SNR in room temperature. In this paper, I firstly applied the time-domain PC sampling technique to the measurement and mapping of picosecond near-field distribution and developed a novel photoconductive near-field (mapping) probe (PCNFP). To do that, I successfully developed an epitaxial lift-off technique originally and applied to the fabrication of the PCNFP to minimize the loading effect [invasiveness]. The resulting probe was 500 $\mu m$ x 420 $\mu m$ fabricated on 1-um-thick LT-GaAs epilayer. The adoption of optical fibers, for guiding laser pulses to the PC switch of the probe and for electrical connections to external apparatus, enabled the probe to be positioned freely with uniform sensitivity. The operation principle of the PCNFP was verified by means of the FDTD simulation: the probe detects the original shape of the incident electromagnetic field by the switching action of the generated carriers in the PC switch of the probe. It is demonstrated in chapter II by means of measurement that the developed PCNFP detects the E-field component with the same direction as that of t...