R. Kiefer

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

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Publications (113)66.39 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Two field plate variants of AlGaN/GaN-HEMTs with and without source-connected field plate (ldquoshieldrdquo) were analyzed for the design of efficient High-Power-Amplifier MMICs operating at X-Band frequencies. This paper presents the design and realization of three dual-stage microstrip MMICs using different device variants for narrowband and broadband applications. Two narrowband HPAs, using GaN HEMTs with and without shield, achieve a maximum output power and PAE of 20 W and >39 %, respectively. A broadband amplifier containing GaN HEMTs without shield reaches a simulated output power beyond 12 W with >30 % PAE over 9-11 GHz.
    Microwave Integrated Circuits Conference, 2009. EuMIC 2009. European; 10/2009
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    ABSTRACT: Amplifiers for the next generation of T/R modules in future active array antennas are realized as monolithically integrated circuits (MMIC) on the basis of novel AlGaN/GaN (is a chemical material description) high electron mobility transistor (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 multi-layer low-temperature cofired ceramic technology (LTCC).
    International Journal of Microwave and Wireless Technologies 07/2009; 1(04):387 - 394. DOI:10.1017/S1759078709990389 · 0.46 Impact Factor
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    ABSTRACT: This paper describes the design and realization of efficient GaN/AlGaN MMICs for X-band frequencies (8 - 12 GHz) in microstrip- transmission-line-technology on 3-inch s.i. SiC substrates. Four dual-stage MMICs are designed and realized based on different bandwidth requirements between 1 GHz and 3 GHz with output power levels of 15 - 20 W at X-band. After optimization of field-plate architectures and driver stage size, a maximum PAE of ges 40% is achieved between 8.5 - 10 GHz with a maximum output power of 19 - 23 W, and an associated power gain of 17 dB. A broadband device with 3 GHz bandwidth reaches ges35% of PAE between 8 and 11 GHz. A 1 mm test chip of the same technology supports a VSWR-ratio test of at least 4:1 at P<sub>-1</sub> <sub>dB</sub> power compression and 10 GHz.
    Microwave Symposium Digest, 2009. MTT '09. IEEE MTT-S International; 07/2009
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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 06/2009; 206(6):1215 - 1220. DOI:10.1002/pssa.200880774 · 1.53 Impact Factor
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    ABSTRACT: The design, realization and characterization of dual-stage X-band high-power and highly-efficient monolithic microwave integrated circuit (MMIC) power amplifiers (PAs) with AlGaN/GaN high electronic mobility transistors (HEMTs) is presented. These high power amplifiers (HPAs) are based on a precise investigation of circuit-relevant HEMT behavior using two different field-plate variants and its effects on PA performance as well as optimization of HPA driver stage size which also has a deep impact on the entire HPA. Two broadband (3 GHz) MMICs with different field-plate variants and two narrowband (1 GHz) PAs with different driver- to final-stage gate-width ratio are realized with a maximum output power of 19-23 W, a maximum power-added efficiency (PAE) of ≥40%, and an associated power gain of 17 dB at X-band. Furthermore, two 1 mm test transistors of the same technology with the mentioned field-plate variants and a 1 mm test MMIC support VSWR-ratio tests of 6:1 and 4:1, respectively.
    Journal of infrared, millimeter and terahertz waves 01/2009; 31(3):367-379. DOI:10.1007/s10762-009-9583-6 · 1.89 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
  • [Show abstract] [Hide abstract]
    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. DOI:10.1002/pssa.200778442 · 1.53 Impact Factor
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    [Show abstract] [Hide abstract]
    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.
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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. DOI:10.1016/j.apsusc.2006.05.091 · 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) 03/2006; 3(3):473 - 477. DOI:10.1002/pssc.200564167
  • [Show abstract] [Hide abstract]
    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 02/2006; 9(1):8-14. DOI:10.1016/j.mssp.2006.01.001 · 1.76 Impact Factor
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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
  • Source
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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; DOI:10.1109/MWSYM.2006.249504

Publication Stats

767 Citations
66.39 Total Impact Points

Institutions

  • 1998–2013
    • Fraunhofer Institute for Applied Solid State Physics IAF
      Freiburg, Baden-Württemberg, Germany
    • Oerlikon Corporate Switzerland
      Pfäffikon (Dorfkern), Zurich, Switzerland
    • Ferdinand-Braun-Institut
      Berlín, Berlin, 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