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202 2009 IEEE International Solid-State Circuits Conference ISSCC 2009 / SESSION 11 / TD: TRENDS IN WIRELESS COMMUNICATIONS / 11.4 11.4 Towards Terahertz Operation of CMOS Swaminathan Sankaran 1,2 ,Chuying Mao 1 ,Eunyoung Seok 1,2 , Dongha Shim 1 , Changhua Cao 1,3 , Ruonan Han 1 , Daniel J. Arenas 1 , David B. Tanner 1 , Stephen Hill 4 , Chih-Ming Hung 2 , Kenneth K. O 1 1 University of Florida, Gainesville, FL, 2 Texas Instruments, Dallas, TX 3 NXP Semiconductors, Austin, TX, 4 Florida State University, Tallahassee, FL The electromagnetic spectrum between 300GHz and 3THz is broadly referred as terahertz [1]. The utility of this portion of spectrum for detection of chem- icals and bio agents, for imaging of concealed weapons, cancer cells and man- ufacturing defects [1, 2], and for studying chemical species using electron paramagnetic resonance, as well as, in short range radars and secured high data rate communications has been demonstrated. However, high cost and low level of integration for III-V devices needed for the systems have limited their wide use. The improvements in the high frequency capability of CMOS have made it possible to consider CMOS as a lower cost alternative for realiz- ing the systems that can greatly expand the use of this spectrum range. A conceptual diagram of a THz spectrometer for chemical detection shown in Fig. 11.4.1 consists of a transmitter with a tunable signal generator and an antenna, and a receiver with an antenna, a detector or a mixer followed by a low noise amplifier/filter. The key components are signal generator, diode detector or mixer, and antennas. This paper reports a new polysilicon gate separated Schottky barrier diode structure (PGS SBD) which enables opera- tion of receivers at frequencies higher than that limited by the transistors; examples of the building blocks with on-chip antennas operating at 100 to 400GHz, which suggest the use of CMOS in THz applications; and a potential path to realize 1THz operation in CMOS. Figure 11.4.2 shows the projected requirements for NMOS unity current gain and power gain frequencies (f T and f max ) from the 2006 International Road Map for Semiconductors (ITRS). It also shows the measured f T and f max in the liter- ature. Despite the concern for the slow down in ITRS, the industry has kept up with the road map to date. The highest f T and f max of bulk transistors are 360 and 420GHz, while the highest f T of SOI transistors is 485GHz. If this can be kept up for another three years, NMOS transistors with f T and f max close to 600GHz will be available. With such devices, amplifiers tuned at 300GHz or at the lower limit of the THz region will be possible. Figure 11.4.3 shows a cross section of new PGS SBD’s fabricated in logic CMOS without any process modifications that can increase the circuit operat- ing frequency beyond that limited by the transistors. The cathode and anode are separated by a polysilicon gate layer. The measured cut-off frequency (f T ) at the 130nm generation is ~2THz. The f T of this diode unlike that of the shal- low trench separated (STS) SBD’s [3] also in Fig. 11.4.3 should scale better
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