Picosecond Electrical Pulse for VLSI Electronics Characterization

Abstract

Picosecond electrical pulses with well resolved frequency components into the terahertz region are ideally suited for the characterization of VLSI electronics, both for the devices themselves and for the interconnect wiring. In this paper, we describe the technology we employ to photoconductively generate and measure these ultrafast electrical signals./1/ A particular emphasis was given to the compatibility with existing VLSI device technology. Although other measurement techniques /2,3/ have shown very good sensitivity and time resolution, the photoconductive sampling technique is particularly attractive for silicon device characterization with a comparable sensitivity and time resolution /4/ and a better amplitude calibration and reproducibility as the sampling geometry is defined by the lithography itself. Impedance matching is facilitated while keeping identical geometries between the device site and the generating and sampling sites. We also present results on the optoelectronic characterization of a 1μm gate GaAs MESFET. We will not address in this paper the problem of circuit testing which has some stringent additional requirements, in particular that of submicron spatial resolution and of wide field addressing capability. These imperatives may ultimately limit the use of purely optical techniques for the functional testing of high speed circuits at their internal nodes.