R. Kiefer

Fraunhofer Institute for Applied Solid State Physics IAF, Freiburg, Baden-Württemberg, Germany

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Publications (111)60.64 Total impact

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    ABSTRACT: We present a systematic study of epitaxial growth, processing technology, device performance and reliability of our GaN HEMTs and MMICs manufactured on 3 inch SiC substrates. Epitaxy and processing are optimized for both performance and reliability. The deposition of the AlGaN/GaN HEMT epitaxial structures is designed for low background carrier concentration and a low trap density in order to simultaneously achieve a high buffer isolation and low DC to RF dispersion. Device fabrication is performed using standard processing techniques involving both electron-beam and stepper lithography. Gate lengths of 250 nm and 500 nm are employed for 10 GHz and 2 GHz applications, respectively. The developed HEMTs demonstrate excellent high-voltage stability, high power performance and large power added efficiencies. Devices exhibit two-terminal gate–drain breakdown voltages in excess of 160 V (current criterion 1 mA/mm) across the entire 3 inch wafer with parasitic gate and drain currents well below 1 mA/mm when biased up to 80 V drain bias under pinch-off conditions. Load-Pull measurements at 2 GHz on 800 μm gate width devices return a well-behaved relationship between bias-voltage and output-power as well as power-added-efficiencies beyond 60% up to UDS = 100 V. For a drain bias of 100 V an output-power-density around 22 W/mm with 26 dB linear gain is obtained. On large devices (32 mm gate width packaged in industry-standard ceramic packages) an output power beyond 100 W is achieved with a PAE above 50% and a linear gain around 15 dB. Dual-stage MMICs in microstrip transmission line technology yield a power added efficiency of 40% at 8.56 GHz for a power level of 11 W. A single-stage MMIC yields a PAE of 46% with 7 W of output power at VDS = 28 V. Reliability is tested on HEMT devices having a gate periphery of 8 × 60 μm at an operating bias of 50 V under both DC and RF conditions. About 10% drain-current change under DC-stress (50 mA/mm) is observed after more than 1000 h of operation with an extrapolated drain-current degradation below 20% after 200000 h (more than 20 years) of operation. Under RF stress (2 GHz, 1 dB compression) the observed change in output power density is below 0.2 dB after more than 1000 h. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
    Physica Status Solidi (A) Applications and Materials 03/2009; 206(6):1215 - 1220. · 1.53 Impact Factor
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    ABSTRACT: This paper describes efficient GaN/AlGaN HEMTs and MMICs for L/S-band (1-4 GHz) and X-band frequencies (8-12 GHz) on three-inch s.i. SiC substrates. Dual-stage MMICs in microstrip transmission-line technology yield a power-added efficiency of ¿40% at 8.56 GHz for a power level of ¿11 W. A single-stage MMIC yields a PAE of ¿55% with 6 W of output power at V<sub>DS</sub>= 20 V. The related mobile communication power HEMT process yields an average power density of 10 W/mm at 2 GHz and V<sub>DS</sub>= 50 V. The average PAE is 61.3% with an average linear gain 24.4 dB and low standard deviation of all parameters. The devices yield more than 25 W/mm of output power at 2 GHz when operated in cw at V<sub>DS</sub>= 100 V with an associated PAE of ¿60%. The GaN HEMT process with 0.5 ¿m gate-length yields an extrapolated lifetime of 10<sup>5</sup> h when operated at V<sub>DS</sub>= 50 V at a channel temperature of 90°C. When operated at 2 GHz devices with 480 ¿m gate-width yield a change of the RF power-gain of less than 0.2 dB under high gain-compression at V<sub>DS</sub>= 50 V and a channel temperature of 250°C.
    Microwave Integrated Circuit Conference, 2008. EuMIC 2008. European; 11/2008
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    ABSTRACT: This paper describes a balanced AlGaN/GaN HEMT single-stage power amplifier demonstrator for X-band frequencies in microstrip line technology on thinned s.i. SiC substrates. The design features a modular circuit concept and microstrip MMIC directional couplers with low impedance levels. These 3 dB-couplers designed for a center frequency of 10 GHz show a coupling factor of 3.5 dB plusmn 0.4 dB and a low net insertion loss of 0.3 dB. The balanced amplifier reaches 11 W pulsed output power at 3 dB compression level and a maximum gain of 10 dB at 8.56 GHz with an input and output match of better than 14 dB from 8.3 to 13 GHz. This 0deg/90deg balanced microstrip AlGaN/GaN HEMT power amplifier MMIC demonstrator may be an interesting alternative to existing hybrid solutions.
    Microwave Integrated Circuit Conference, 2008. EuMIC 2008. European; 11/2008
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    ABSTRACT: Amplifiers for a next generation of T/R-modules in future active array antennas are realized as monolithically integrated circuits (MMIC) on the bases of novel AlGaN/GaN HEMT structures. Both, low noise and power amplifiers are designed for X-band frequencies. The MMICs are designed, simulated and fabricated using a novel via-hole microstrip technology. Output power levels of 6.8 W (38 dBm) for the driver amplifier (DA) and 20 W (43 dBm) for the high power amplifier (HPA) are measured. The measured noise figure of the low noise amplifier (LNA) is in the range of 1.5 dB. A T/R-module front-end with mounted GaN MMICs is designed based on a multilayer LTCC technology.
    Microwave Integrated Circuit Conference, 2008. EuMIC 2008. European; 11/2008
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    ABSTRACT: We report on device performance and reliability of our 3″ GaN high electron mobility transistor (HEMT) technology. AlGaN/GaN HEMT structures are grown on semi-insulating SiC substrates by metal-organic chemical vapor deposition (MOCVD) with sheet resistance uniformities better than 2%. Device fabrication is performed using standard processing techniques involving both e-beam and stepper lithography. AlGaN/GaN HEMTs demonstrate excellent high-voltage stability and large efficiencies. Devices with 0.5 µm gate length exhibit two-terminal gate-drain breakdown voltages in excess of 160 V and drain currents well below 1 mA/mm when biased at 80 V drain bias under pinch-off conditions. Load-pull measurements at 2 GHz return both a linear relationship between drain bias voltage and output power as well as power added efficiencies beyond 55% up to 72 V drain bias for which an output power density of 9 W/mm with 25 dB linear gain is obtained. Reliability tests indicate a promising device stability under both radio frequency (RF) and direct current (DC) stress conditions. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
    Physica Status Solidi (A) Applications and Materials 04/2008; 205(5):1078 - 1080. · 1.53 Impact Factor
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    ABSTRACT: We report on device performance and reliability of our 3′′ GaN HEMT technology. AlGaN/GaN HEMT structures are grown on semi-insulating SiC substrates by MOCVD with sheet resistance uniformities better than 3%. Device fabrication is performed using standard processing techniques involving both e-beam and stepper lithography. The process technology exhibits an excellent uniformity across a single wafer as well as high reproducibility between individual wafers of the same or a different batch. Loadpull mapping of 8×400 μm gate periphery devices with 0.5 μm gate length across all 21 cells on entire 3-inch wafers yields a PAE of (60±2)% with only 2% scatter of the mean PAE from wafer to wafer. AlGaN/GaN HEMT's demonstrate superior high-voltage stability and large efficiencies. Devices with 0.5 μm gate length exhibit two-terminal gate-drain breakdown voltages in excess of 160 V and drain currents well below 1 mA/mm when biased at 80 V drain bias under pinch-off conditions. Load-pull measurements at 2 GHz return both a linear relationship between drain bias voltage and output power as well as power added efficiencies beyond 60% up to 80 V drain bias. At 88 V an output power density of 15 W/mm with 24 dB linear gain is obtained. Reliability tests indicate a promising device stability under both radio frequency (RF) and direct current (DC) stress conditions.
    01/2008;
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    ABSTRACT: Group III-nitride based heterostructures are of rapidly growing importance for the fabrication of short-wavelength light-emitting devices as well as for high-power high-frequency field effect transistors. Design and modeling of high-performance devices requires the precise knowledge of basic (AlGaIn)N material parameters. First, the composition dependence of the AlGaN and InGaN band gap energy will be addressed. Second, available data on the band offsets between GaN and AlGaN as well as GaN and InGaN will be discussed, which are important parameters for the design of GaN/AlGaN and InGaN/GaN hetero- and quantum well (QW) structures. Next, the effect of built-in strain and resulting piezoelectric fields on the luminescence properties of InGaN/GaN quantum wells will be addressed, including implications for an optimization of the InGaN QW width for light-emitting diode (LED) applications. Finally, results on GaN/InGaN/AlGaN QW LEDs emitting in the violet spectral region will be presented.
    10/2007: pages 641-656;
  • 05/2007: pages 131-157;
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    ABSTRACT: Structural defects and their impact on the performance, lifetime and reliability of electronic devices are of permanent interest for crystal growers and device manufacturers. This is especially true for epitaxial (Al, Ga)N / GaN based high electron mobility transistor (HEMT) structures on 4H-SiC (0001) substrates. This work points out how micropipes, dislocations and grain boundaries present in a 4H-SiC (0001) wafer and subsequently overgrown with an (Al,Ga)N - GaN - HEMT layer sequence show up in X-ray topographic images and two-dimensional XRD maps. Using X-ray topography in transmission geometry, micropipes and other structural defects are localized non-destructively below structured metallization layers with a spatial resolution of a few tens of micrometers.
    Applied Surface Science 10/2006; 253(1):209-213. · 2.54 Impact Factor
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    ABSTRACT: High power amplifiers for a next generation of T/R-modules for future X-band active array antennas are realized on the bases of novel AlGaN/GaN HEMT structures, which are epitaxially grown on SiC wafer substrates. Both, hybrid and monolithically integrated circuits are designed and realized as key elements for transmit chains. Based on hybrid designs excellent peak power levels of 23 W (43.6 dBm) with an associated power added efficiency (PAE) of 29% are realized. Over a bandwidth of 2 GHz (X-band) the output power levels are above 20 W. In a more sophisticated approach first monolithically integrated circuits (MMICs) are designed, simulated and fabricated using a novel via-hole microstrip technology. Output power levels of 20 W (43 dBm) with an associated PAE of 30% are measured on small size 12 mm<sup>2</sup> chips. Highest ever reported maximum power added efficiency values of up to 36.5% are achieved
    Microwave Symposium Digest, 2006. IEEE MTT-S International; 07/2006
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    ABSTRACT: AlGaN/GaN-based HEMT MMICs on s.i. SiC wafer substrates are designed and realized for linear broadband amplifiers. Electrical performance data and assembly technology issues are presented in this paper. The linear broadband amplifier MMIC operates in the frequency range from 9 GHz to 19 GHz and is fabricated in microstrip technology including via-holes. The measured small signal gain is about 13 dB and the output power at 1dB compression is in the range of 27dBm. Two-tone measurements show good linearity. Up to 26dBm output power the IM3 value is better than 30dBc. A reliable assembly process for the MMICs is necessary in order to achieve good thermal conductivity between the underlying SiC wafer substrate and the heatspreader beneath
    Microwave Symposium Digest, 2006. IEEE MTT-S International; 07/2006
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    ABSTRACT: This work presents very recent examples for the realization of high-power amplifiers for both communication and solid-state radar applications based on AlGaN/GaN HEMTs on s.i. SiC substrate. Broadband power amplifiers for mobile communication base stations between 0.9 and 2.7 GHz are presented. Microstrip line X-frequency band power amplifiers provide pulsed output power levels of 10 W with 16 dB of gain at 9 GHz. This work further shows improved device reliability results at VDS = 30 V and 200 °C channel temperature for gate lengths of 300 nm. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
    physica status solidi (c) 02/2006; 3(3):473 - 477.
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    ABSTRACT: This work describes the operation of AlGaN/GaN HEMTs on s.i. SiC substrate in a broadband AlGaN/GaN push-pull amplifier for 3G/4G infrastructure applications between between 1.8 GHz and 2.2 GHz. The device yields linear gain of 12.9 dB, a 3 dB bandwidth of 400 MHz between 1.8 GHz and 2.2 GHz, and a maximum output power of 102 W at 1.95 GHz under single carrier 16 channel W-CDMA conditions. Linearity evaluation further yields a peak output power of 45 dBm for an ACLR of -45 dBc at 5 MHz offset at 1.95 GHz
    Electron Devices Meeting, 2005. IEDM Technical Digest. IEEE International; 01/2006
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    01/2006;
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    ABSTRACT: Structural defects and their impact on the performance of electronic devices are of permanent interest for crystal growers and device manufacturers. This is especially true for epitaxial (Al,Ga)N/GaN-based high electron mobility transistor structures on 4H-SiC (0001) substrates. This work concentrates on the recognition and imaging of defects in (Al,Ga)N/GaN/4H-SiC(0001) heterostructures accomplished non-destructively by three X-ray diffraction techniques. X-ray topography and X-ray Bragg angle mapping are compared with respect to the spatial resolution of the defects. X-ray curvature measurements are used to quantify long-ranging stresses in the heterostructure during device fabrication.
    Materials Science in Semiconductor Processing 01/2006; 9(1):8-14. · 1.34 Impact Factor
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    ABSTRACT: This work describes AlGaN/GaN power amplifier MMICs in microstrip line technology on s.i. SiC substrate for X-band frequencies with output power levels well beyond 15 W. A dual-stage design supplies 18 dB of gain at 10 GHz with a pulsed output power of 20 W at VDS= 40 V. Further, a single-stage MMIC with 6 mm gate width provides a P-1dB of 14.5 W and a maximum output power of 22.4 W, also at 10 GHz
    IEEE MTT-S International Microwave Symposium digest. IEEE MTT-S International Microwave Symposium 01/2006;
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    ABSTRACT: A dry etch process based on Cl2/SF6 has been developed to selectively remove GaN over AlGaN for the fabrication of recessed gate GaN/AlGaN HEMTs. Using this etching process recessed and non-recessed FETs were fabricated side by side on the same wafer to provide a fair comparision of data. Recessed gate FETs with a gatelength of 0.15μm show cutoff frequencies of 83 and more than 200 GHz for fT and fmax, respectively. Furthermore, gate-drain breakdown as high as 84V has been obtained which is more than twice as much compared to their non-recessed counterparts.
    MRS Proceedings. 12/2005; 955.
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    ABSTRACT: GaN HFETs have been proposed for high power high linearity and high bandwidth applications and reached tremendous output power levels (Kikkawa et al., 2004). However, there are relatively few circuit examples especially for wideband power amplifiers fulfilling the requirements of future multiband/multistandard capable 3G/4G base stations. This work presents first promising results of realised GaN based wideband power amplifier demonstrators for the mentioned field of application. Two different amplifier concepts for the final stage of a power amplifier module for medium range multiband base station applications in the L- and S-Band have been implemented as first amplifier demonstrators. The amplifiers have been characterized by using single carrier W-CDMA signals and showed a promising high bandwidth for output power levels up to > 10 W while meeting the 3GPP ACLR specification in a wide frequency range.
    Microwave Conference, 2005 European; 11/2005
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    ABSTRACT: A two-stage high-power amplifier MMIC was realized with a chip size of 4.5 mm /spl times/ 3 mm operating between 8 GHz and 10 GHz based on a fully integrated microstrip AlGaN/GaN HEMT technology on s.i. SiC substrate. The MMIC device delivers a maximum pulsed output power of 8.9 W (39.5 dBm) at 8.5 GHz at V/sub DS/ = 31 V, 10 % duty cycle, and more than 6 dB gain compression level, and features a linear gain in excess of 20 dB.
    Gallium Arsenide and Other Semiconductor Application Symposium, 2005. EGAAS 2005. European; 11/2005
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    ABSTRACT: Broadband microstrip and coplanar MMIC amplifiers featuring beyond 10 W for X-band radar applications are realized in a AlGaN/GaN HEMT technology on 2" s.i. SiC substrate. Single-stage and dual-stage demonstrators with flat gain from 1 GHz to 2.7 GHz and up to 40 W peak power in hybrid microstrip technology for basestation applications are presented. The performance illustrates the potential of this technology with very high bandwidth and superior power density in comparison to GaAs.
    Gallium Arsenide and Other Semiconductor Application Symposium, 2005. EGAAS 2005. European; 11/2005

Publication Stats

464 Citations
60.64 Total Impact Points

Institutions

  • 1999–2012
    • Fraunhofer Institute for Applied Solid State Physics IAF
      Freiburg, Baden-Württemberg, Germany
  • 2008
    • United Monolithic Semiconductors
      Ulm, Baden-Württemberg, Germany
  • 2006
    • Universität Stuttgart
      • Institute of Electrical and Optical Communication Engineering
      Stuttgart, Baden-Wuerttemberg, Germany
  • 2002
    • University of Hamburg
      • Institut für Laserphysik
      Hamburg, Hamburg, Germany