High temperature superconducting multilayer multichip module: fabrication and high speed characterization

Superconductivity is attractive for high performance multichip modules (MCMs) for increasing wiring density while eliminating attenuation and dispersion caused by wiring resistance. However, multilayer HTS structures have been difficult to fabricate. A methodology and materials set was developed to fabricate a multilayer structure with superconducting traces in the X-Y planes and normal metal interconnects in the Z-plane. A simple, multilayer circuit was designed to characterize the high-speed digital waveform characteristics and pulse integrity. Design guidelines were employed to maintain constant impedance through multiple transmission lines. The circuit was modeled on a 3D simulator with a one nanosecond rise-time pulse. The goal was to correlate the modeled and measured data with respect to the pulse integrity and impedance. Eye-diagrams were produced using a one-gigahertz pulse train. In addition, thermal cycling was performed on the structures to identify if any thermal expansion mismatches occurred. Electrical tests were performed before and after the cycling to verify circuit integrity. The data from the thermal cycling will be discussed.