SGER: Investigation of Microwave Components on CMOS Substrate for a Wireless Chip-to-Chip Interconnect System

University Of Arizona, Tucson AZ

Investigators

Abstract

0095245 Papapolymerou Microwave and mm-wave circuit technology that offers high-performance, low cost, small size and high profit is essential for today's cost driven commercial and military industries. In order to meet the above requirements, the research community during the last five years has been focusing on entire system-on-a-chip solutions, where both passive and active components are monolithically integrated on a single semiconductor substrate (Si, GaAs, SiGe) for dense, miniature lightweight and highly reliable microwave systems. The above solutions will also lead to analog, digital, MEMS and microwave circuits co-existing on a single chip that is capable to sense, think, act and communicate. This concept can be used for the development of microwave/mm-wave circuit-to-circuit interconnects that overcome many of the problems associated with traditional interconnect techniques and address future demands for feature sizes less than 100 nm. Currently, wire bond and flip chip interconnects are large compared to dimensions used in microelectronic fabrication technologies and cannot meet the signal delay and clock speed requirements beyond the 100 mn node. Guided-wave interconnects using metal traces also pose serious limitations due to propagation delay, signal distortion, noise and losses. Furthermore, they impose a serious limitation on circuit density and cost and can introduce parasitic reactances that degrade circuit performance. Wireless interconnects, on the other hand, eliminate the need for increased wire density and do not suffer from loss related to finite interconnect conductivity. Parasitic effects, such as crosstalk, are reduced and time delays can also be minimized if a fast conversion scheme that translates the base signal to an RF one is used. In this project, the PI proposes to investigate both theoretically and experimentally the basic microwave components of a wireless chip-to-chip interconnect system operating between 30 and 35 GHz. These components will reside on top of a low resistivity (CMOS) silicon wafer covered with a thin dielectric layer such as polyimide. The microwave circuits will be designed with Finite Ground Coplanar (FGC) line elements that can support TEM mode propagation and have a loss that is predominantly ohmic. The philosophy of the system is the following: An oscillator at 30-35 GHz will feed a planar phase shifter that utilizes MEMS bridges to change the phase of the microwave signal that is then transmitted by a slot antenna. The digital bit stream is applied as a positive modulating voltage to the MEMS phase shifter producing a microwave signal with BPSK modulation. At the receiving chip the phase of the incoming microwave signal (received with a slot antenna) will be compared to a reference signal via a phase detector (mixer) that will demodulate the BPSK microwave signal. A bandpass filter is used right after the receiving slot antenna to isolate the frequency of interest. Due to the high risk nature of the proposed research, the study of three passive components (slot antenna, MEMS phase shifter and bandpass filter) on CMOS silicon wafers will be pursued under an SGER grant. The three microwave circuits will be characterized experimentally with on-wafer measurements and theoretically with full-wave simulations. The main research effort will focus on understanding the properties and performance implications and limitations of the three passive microwave circuits residing on top of a low resistivity silicon substrate, with a goal to optimize their response. For the phase shifter, the characteristics of the MEMS switches on top of a CMOS wafer will also be explored and their interaction with it will be analyzed. It is anticipated that the proposed research will result in significant contributions to the area of integrated microwave and digital systems-on-a-chip and wireless interconnects, as well as provide valuable insights for the design of FGC microwave circuits on CMOS substrates used for digital circuitry.