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 photoconductors 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.