Golden Bump Based Flip-Chip Interconnection for Superconducting Multi-Chip Module

This paper introduces the preparation of golden bumps on the single flux quantum (SFQ) circuit chip by using the 20-μm-diameter golden wire and the flip-chip (FC) bonding of the SFQ chip and the substrate by the ultrasonic bonding method. Firstly, a coplanar waveguide (CPW) flip-chip interconnect structure was designed and fabricated, and the low-temperature transmission performance i.e., S-parameters were tested. The results showed that
S
₁₁
≤ −10 dB and
S
₂₁
≥ −3 dB among the range from 100 MHz to 52 GHz at 4.2 K. And the golden bump can transmit PRBSs of 5 Gbps, and its bit error rate (BER) is less than 10
⁻¹²
. Secondly, the flip-chip bonded SFQ driver& receiver circuits with 4.7-Ohm impedance were prepared and the BER of the SFQ pulse signals were measured by the driver& receiver circuits. The test results showed a zero-bit error rate when the number of transmitted codes is in the order of 10
⁶
. The experimental results show that the golden bump based flip-chip interconnection has good high-frequency transmission performance, and can be used for high-bandwidth and narrow pulse signal transmission in superconducting multi-chip modules (MCMs).