On-Chip Picosecond Time-Domain Measurements for VLSI and Interconnect Testing Using Photoconductors

Picosecond time-domain measurements of silicon IC interconnects were successfully performed using photoconductors integrated on-chip. Standard IC fabrication techniques followed by shadow-masked ion-beam irradiation were used to create the photoconductor/interconnect structures. Starting materials used were 70-Ω˙cm n-type wafers and 16-Ω˙cm p-type wafers. A subpicosecond pulsed laser system excited the photo-conductors to produce and sample picosecond pulses on the Si substrate. These integrated photoconductors can also be used to perform picosecond transient measurements of VLSI devices and circuits. Optoelectronic cross-correlation measurements with photoconductor pulsers and photoconductor sampling gates were performed to characterize both the on-chip photoconductors and the on-chip interconnects. Photoconductors processed as pulsers produced electrical pulses with ~ 2-ps rise time, ~ 200-mV peak amplitude and full width at half-maximum (FWHM) of < 10 ps. Photoconductors processed as sampling gates demonstrated 3-dB measurement bandwidths of 20 GHz. Due to the absence of jitter on-chip signal delays were measured with subpicosecond precision.