Abstract-The feasibility of integrating antennas and required circuits to form wireless interconnects in foundry digital CMOS technologies has been demonstrated. The key chal- lenges including the effects of metal structures associated with integrated circuits, heat removal, packaging, and inter- action of transmitted and received signals with nearby cir- cuits appear to be manageable. Besides, on-chip interconnection, this technology can potentially be applied for implementation of true single chip radio and radar, inter- chip communication systems, RFID tags and others. Introduction Scaling of MOS transistor length to below 0.10 µm has made the implementation of CMOS circuits operating at 20 GHz and higher feasible [1]-[4]. In fact, according to the 2003 International Road Map for Semiconductor (ITRS) [5], the cut-off frequency (f T ) and unity maximum available power gain frequency (f max ) targets for the year 2015 are ~ 700 GHz. With such transistors, it should be possible to implement RF circuits operating at 200-250 GHz. At 24 GHz, the wavelength of electro-magnetic waves in free space is 12.5 mm and in silicon it is 3.7 mm. This means a quarter wave antenna needs to be only ~ 3 and 0.9 mm in free space and silicon. These in conjunction with the increases of chip sizes to ~ 2 cm x 2 cm have made the integration of antennas for wireless communication possible. On-chip antennas could potentially be used to relieve the bottleneck associated with global signal distribution inside integrated circuits (IC’s). Wireless interconnects using on- chip antennas could lower clock skew [6] and reduce the impact of dispersion (Fig. 1) besides freeing up wiring resources for other uses. On-chip antennas could also be used for data communication among integrated circuits to lower the I/O pin counts, thus reducing the form factor and packag- ing costs (Fig. 2) [7], as well as for communication within an IC. By incorporating a technique for eliminating the need for an off-chip crystal reference [8] into a transceiver with on- chip antennas [9],[10], a true single chip radio which is small, reliable and easy to use can also be realized. The availability of sensor nodes incorporating such a radio (µ-nodes, Fig. 3) will accelerate the realization of the Smart Dust vision [11]. This paper reviews the status of key technologies required to implement on-chip and inter-chip wireless interconnect systems as well as challenges and potential solutions. This paper discusses the paths for signal propagation [12], perfor- mance of integrated antennas on 10-20 Ω-cm silicon sub- strates commonly used in CMOS and BiCMOS technologies [13]-[15], circuits which could be implemented in main- stream CMOS technologies for these applications [16],[17] and demonstrations of wireless interconnects [18],[19]. The key challenges including the effects of metal structures asso- ciated with integrated circuits [20]-[23], heat removal [18], packaging [19], and interaction of transmitted and received signals with nearby circuits [24]-[27] are discussed. Figure 4 shows some of the possible paths for signal propa- gation within an integrated circuit. There are a direct path, a Frequency Divider LNA Matching Circuit Buffers Buffer Sector Output to Local System Fig.1: Wireless Clock Receiver Block Diagram RX TX RX RX RX RX RX RX RX RX RX RX RX RX RX RX RX RX=Receiver TX=Transmitter IC edge clock signal Integrated Circuits (PC Board/MCM) transmitted Z S Receiving Antennas Transmitting Antenna (with parabolic reflector) PC board using wireless I/O’ Conventional PC Chip Packa g e Fig. 2. A printed circuit board with circuits utilizing wireless interconnects. The Feasibility of On-Chip Interconnection using Antennas K. K. O, K. Kim, B. Floyd, J. Mehta, H. Yoon, C.-M. Hung, D. Bravo, T. Dickson, X. Guo, R. Li, N. Trichy, J. Caserta, W. Bomstad, J. Branch, D.-J. Yang, J. Bohorquez, J. Chen, E.-Y. Seok, L. Gao, A. Sugavanam, J.-J. Lin, S. Yu, C. Cao, M.-H. Hwang, Y.-P. Ding, S.-H. Hwang, H. Wu, N. Zhang, and J. E. Brewer Silicon Microwave Integrated Circuits and System Research Group (SiMICS) Department of Electrical and Computer Engineering, University of Florida, Gainesville, FL, 32611 Tel.: 352-392-6618, e-mail: kko@tec.ufl.edu 0-7803-9254-X/05/$20.00 ©2005 IEEE. 979