Abstract
Connecting chips within a module is a basic requirement in transforming MMIC performance to system functionality. More and more applications demand for operation at high mm-wave frequencies or with ultra-large bandwidth. While semiconductor devices have seen tremendous progress in terms of their frequency limits, the chip interconnects lag behind and often form the bottleneck in realizing such systems. This paper reviews the broadband potential of the most common interconnect types in use and their performance demonstrated so far, covering wirebonding, approaches with chips embedded in a substrate, and flip-chip. Additionally, as an intermediate solution between system-on-chip and system-in-a-package, semiconductor hetero-integration on the chip-level is included. As is discussed, bond wire interconnects are most limited in bandwidth among the four types and reach the 100 GHz band only at the expense of narrowband characteristics. Dedicated embedded-chip packaging techniques show significantly better performance, bandwidths in the order of 100 GHz have been shown in the literature. Flip-chip has clearly the highest potential, interconnects covering the range from DC to 500 GHz have been demonstrated and are presented in the paper. Hetero-integration on the chip proves to allow for very broadband interconnects between elements and circuits on the compound chip as well: For an InP-on-BiCMOS process 325 GHz bandwidth were achieved and even higher values seem to be feasible.
Highlights
The frequency limits of semiconductor technologies have seen a continuous improvement over the past decades
Operation frequencies in the 300 GHz range are accessible with several technologies, from RFCMOS and SiGe-BiCMOS to InP technologies, and even GaN is entering this arena
The development of packaging has not kept pace with the progress in semiconductor technology and the interconnects between different chips have become a major obstacle in realizing the high-frequency and broadband systems targeted [5]
Summary
The frequency limits of semiconductor technologies have seen a continuous improvement over the past decades. In order to circumvent this bottleneck in packaging, systemon-chip (SoC) solutions have been applied, combining the entire high-frequency part of a system on a single chip, avoiding any critical off-chip connection This requires a semiconductor process with universal capabilities for all transmit and receive functionalities, including antennas and optical components, for instance. The required set of specifications is difficult to fulfill with a single technology and, the availability of chip interconnects with high bandwidth remains an essential requirement in many applications This is the basic motivation for this paper. The state of the art in the most common approaches will be presented and their bandwidth potential discussed This includes relevant own results using flip-chip technology and hetero-integration on chip level. The conclusions summarize the outcome and identify general trends
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