High aspect ratio lines as low distortion, high frequency off-chip interconnects

Achieving dense off-chip interconnection with satisfactory electrical performance is emerging as a major challenge in advanced system engineering. High aspect ratio (HAR) lines, which consist of tall, narrow conductors, are proposed as high frequency off-chip interconnects. They offer low distortion transmission at higher density than striplines. For example, a 35-Ω 5:1 height-to-width differential HAR line could achieve <0.6-dB/cm loss at 1 GHz at a pitch of ~32 μm, commonly achieved only for single-ended lines; as for any differential line, such a differential HAR line would be less prone to Δ-I noise and external interference. Design of HAR lines, including trade-offs between fabrication difficulty and density increase, is discussed. HAR lines were fabricated at a pitch of 30 μm, requiring an aspect ratio of 3 for ~50-Ω characteristic impedance, ⩽0.6-dB/cm loss at 1 GHz, and <5% near-end crosstalk