C. KOO Millimeter-wave Integrated Systems Lab. RF Power Transistors For Mobile Applications 전기공학부 구찬회

C. KOO Millimeter-wave Integrated Systems Lab. Background In general, signals with lower frequency can penetrate walls better. But antenna size varies with RF wavelength, so low-frequency RF is not practical for handheld devices. In addition, frequencies of RF noises are ranging from MHz, so frequencies > 3000 MHz is better. History of RF Transistors Many different types of RF transistors available: -Bipolar: Si BJTs, SiGe HBTs, III-V HBTs -FET: GaAs MESFETs, III-V HEMTs, Wide Bandgap HEMTs, Si MOSFETs

C. KOO Millimeter-wave Integrated Systems Lab. Operating Frequencies of Widely Used RF Electronics qMost RF systems having real mass markets operate under 5 GHz. qCellular phones(GSM, CDMA) - 900MHz,1.8 and 1.9GHz qFuture 3G cellular phones (CDMA2000, Wideband CDMA) - 3GHz qAdvanced mobile communications - GPS(global positioning systems) - 1.8GHz - GPRS(general packet radio service) - 2.5GHz qWireless local area network (Bluetooth) GHz qCollision avoidance radar used in automobiles - 77 GHz qMicrowave oven GHz

C. KOO Millimeter-wave Integrated Systems Lab. RF Transistor Figures of Merit qCutoff Frequency f T Frequency at which the magnitude of the short circuit current gain h21 rolls off to 1 (0 dB). qMax Frequency of Oscillation f max Frequency at which the unilateral power gain U rolls off to 1 (0 dB). qf T and f max can be extracted from h21 and U roll off at higher frequencies at a slope of –20 dB/dec. Further RF Transistor FOMs : NFmin, Pout, PAE, MAG

C. KOO Millimeter-wave Integrated Systems Lab. HBT (1)

C. KOO Millimeter-wave Integrated Systems Lab. HBT (2) HBT Types GaAs HBT InP HBT SiGe HBT Design Features Wide bandgap emitter Narrow bandgap base Thin base (less than 0.1 μm) High base doping GaAs-based HBT has been the most widely used HBT in RF design, but SiGe HBT has gained popularity recently due to its superior noise performance and its compatibility with existing Si CMOS technology.

C. KOO Millimeter-wave Integrated Systems Lab. HEMT (1) HEMT: High Electron Mobility Transistor

C. KOO Millimeter-wave Integrated Systems Lab. HEMT (2) Design Features Deep sub-µm gate Mushroom gate Very short gate length High mobility channel layer Large conduction band offset 2DEG HEMT Types AlGaAs/GaAs HEMT InP HEMT AlGaN/GaN HEMT Importance of metamorphic HEMT (mHEMT) will continue to grow. -The key feature of this device is an InGaAs layer grown on GaAs substrate with an In content higher than that in GaAs pHEMT. -The main advantge of this approach is inexpensive GaAs substrate can be used to obtain InP HEMT like performance.

C. KOO Millimeter-wave Integrated Systems Lab. Power Amplifiers for Mobile Communication Systems (1) qCellular PA -Current PA : 95% with GaAs -New Comers : SiGe PA & CMOS PA (skeptical) -SiGe BICMOS : better for integration better for cost (?) (Triquint claimed that GaAs has 15% less cost) -Issues : SoC or SoP qWireless LAN -Competitive technologies same with cellular PA -IEEE g(2.4GHz, 54Mbps) & IEEE a(5GHz, 54Mbps) -67% of 177M PAs from GaAs in 2008 (Strategy Analytics) qCellular Base Stations -90% market with LDMOS -Competitive Technologies : GaN HFET(reliability), GaAs PHEMT qSwitch – mainly with GaAs PHEMT

C. KOO Millimeter-wave Integrated Systems Lab. Power Amplifiers for Mobile Communication Systems (2) Technologies for GaN HEMTs are not yet mature, but devices with f T and f max exceeding 100 GHz and very high output power densities have been demonstrated. Wide bandgap FETs(SiC MESFET& GaN HEMT) show the highest output power densities of all RF FETs in the frequency range important for currentmobile communication sytems (up to 5 GHz)

C. KOO Millimeter-wave Integrated Systems Lab. Trend of RF Transistors qImportant Trends Continuous increase of the frequency limits, i.e. f T and f max Development of low- cost RF transistors for mass onsumer markets “InP HBT and HMET possess the best frequency performance” But, the technology for InP-based devices is not yet mature. These devices alsohave poorer power performance.

C. KOO Millimeter-wave Integrated Systems Lab. References qRF and Microwave Power Amplifier and Transmitter Technologies- Frederick H. Raab, Peter Asbeck, Steve Cripps, Peter B. Kenington, Zoya B. Popovic, Nick Pothecary, John F. Sevic and Nathan O. Sokal qF. Schwierz and J. J. Liou, Modern Microwave Transistors – Theory, Design, and Applications, J. Wiley 2002 qL. D. Nguyen et al., Ultra-High-Speed Modulation-Doped Field-Effect Transistors,Proc. IEEE, 80, p qD. Halchin, M. Golio, Trends for Portable Wireless Applications, Microwave J., Jan. 1997, p. 62 qF. Schwierz and J. J. Liou, Semiconductor Devices for RF Applications: Evolution and Current Status, Microel. Rel