SiC Transistors Research Articles

Pulse input Class-C power amplifier response of SiC MESFET using physical transistor structure in TCAD

The switching behavior of a previously fabricated and tested SiC transistor is studied in Class-C amplifier in TCAD simulation. The transistor is simulated for pulse input signals in Class-C power amplifier. The simulated gain (dB), power density (W/mm) and power added efficiency (PAE%) at 500 MHz, 1, 2 and 3 GHz was studied using computational TCAD load pull simulation technique. A Maximum PAE of 77.8% at 500 MHz with 45.4 dB power gain and power density of 2.43 W/mm is achieved. This technique allows the prediction of switching response of the device for switching amplifier Classes (Class-C–F) before undertaking an expensive and time consuming device fabrication. The beauty of this technique is that, we need no matching and other lumped element networks for studying the large signal behavior of RF and microwave transistors.

High-Temperature Operation of SiC Power Devices by Low-Temperature Sintered Silver Die-Attachment

In this paper, we present the realization of high-temperature operation of SiC power semiconductor devices by low-temperature sintering of nanoscale silver paste as a novel die-attachment solution. The silver paste was prepared by mixing nanoscale silver particles with carefully selected organic components which can burn out within the low-temperature firing range. SiC Schottky diodes were placed onto stencil-printed layers of the nanoscale silver paste on Au or Ag metallized direct bonded copper (DBC) substrates for the die-attachment. After heating up to 300degC and dwell for 40 min in air to burn out the organic components in the paste and to sinter the nanoscale silver, the paste consolidated into a strong and uniform die-attach bonding layer with purity >99% and density >80%. Then the die-attached SiC devices were cooled down to room temperature and their top terminals were wire-bonded to achieve the high-temperature power packages. Then the power packages were heated up from room temperature to 300degC for high-temperature operation and characterization. Results of the measurement demonstrate the low-temperature silver sintering as an effective die-attach method for high-temperature electronic packaging. An advanced packaging structure for future SiC transistors with several potential advantages was also proposed based on the low-temperature sintering technology.

Novel material concepts of transducers for chemical and biosensors

The objectives of this work are to contribute to the knowledge about physical and chemical properties of WBG semiconductors, such as ZnO and GaN towards development of advanced bio- and chemical sensors. For the semiconductors, growth techniques typically yielding single crystal material are applied. Thin epitaxial quality films of ZnO and GaN are fabricated on SiC or sapphire substrates. An emphasis is given to ZnO due to the interesting combination of the semiconductor and oxide properties. Surface bio-functionalization of ZnO is performed by APTES, MPA or MP-TMS molecules. We have compared some of the results to (hydroxylated) GaN surfaces functionalized by MP-TMS. The covalent attachment of the self-assembled biomolecular layers has been proven by XPS analysis. For complementary electrical characterization impedance spectroscopy measurements were performed. The results are intended to serve the realization of bioelectronic transducer devices based on SiC or GaN transistors with a ZnO gate layer.To take advantage of the catalytic properties of ZnO, initial prototypes of chemical sensors for gas sensing are processed on ZnO deposited either on SiC or on sapphire and they are further tested for the response to reducing or oxidizing gas ambient. The sensor devices show sensitivity to oxygen in the surface resistivity mode while a Pt Schottky contact ZnO/SiC device responds to reducing gases. These results are compared to published results on Pt/GaN Schottky diodes.

Investigation of the SiC Transistor and Diode Nuclear Detectors at 8 MeV Proton Irradiation

Nuclear-particle detectors based on SiC with a structure composed of an n+-type substrate, a p-type epitaxial layer, and a Schottky barrier are studied. Structures with a ~10-µm-thick 6H-SiC layer exhibit transistor properties, whereas those with a ~30-µm-thick 4H-SiC layer exhibit diode properties. It is established that a more than tenfold amplification of the signal is observed in the transistor-type structure. The amplification is retained after irradiation with 8-MeV protons with a dose of at least 5 × 10 13 cm –2 ; in this case, the resolution is ≤ 10%. Amplification of the signal was not observed in the structures of diode type. However, there were diode-type detectors with a resolution of ≈ 3%, which is acceptable for a number of applications, even after irradiation with the highest dose of 2 × 10 14 cm.

Next generation SiC transistors

PowerSicel Inc, a University of Colorado, Boulder, spinoff has won a NIST Advanced Technology Programme award to develop new, high power transistors, operating at 10× power density and 5× efficiency of conventional power transistors, enabling broadband ultra linear power amplifiers for cellular and satellite communication, radar, TV broadcast, industrial instruments and medical equipment. This is a short news story only. Visit www.three-fives.com for the latest advanced semiconductor industry news.

SiC microwave power technologies

Two SiC transistors that are investigated for microwave power applications are the 4H-SiC static induction transistor (SIT) and the 4H-SiC metal-semiconductor field-effect transistor (MESFET). Ultrahigh frequency 4H-SiC SITs have demonstrated record-breaking pulsed power per package (900 W) with excellent associated power-added efficiency (PAE) of 78%. S band 4H-SiC MESFETs have shown a record power-density of 5.6 W/mm and 36% PAE, as well as 80 W continuous-wave (CW) power (1.6 W/mm), with an associated PAE of 38%. X-band MESFET power density of 4.3 W/mm was obtained for exploratory CW devices. These performance gains are afforded by the advantageous material properties of silicon carbide. SiC SIT technology offers many military system advantages including lower cost, lower weight, higher power and high temperature of operation and higher efficiency transmitters with minimal cooling requirements. SiC RF MESFET's and circuits are candidates for use in efficient linear transmitters for commercial and military communications.

High density plasma via hole etching in SiC

Throughwafer vias up to 100 μm deep were formed in 4H-SiC substrates by inductively coupled plasma etching with SF6/O2 at a controlled rate of ∼0.6 μm min−1 and use of Al masks. Selectivities of >50 for SiC over Al were achieved. Electrical (capacitance–voltage: current–voltage) and chemical (Auger electron spectroscopy) analysis techniques showed that the etching produced only minor changes in reverse breakdown voltage, Schottky barrier height, and near surface stoichiometry of the SiC and had high selectivity over common frontside metallization. The SiC etch rate was a strong function of the incident ion energy during plasma exposure. This process is attractive for power SiC transistors intended for high current, high temperature applications and also for SiC micromachining.

A review of junction field effect transistors for high-temperature and high-power electronics

The status of GaAs, SiC and GaN junction field effect transistors (JFETs) is reviewed with a focus on their application to high temperature and high power operation. The advantage of the JFET structure for this operation regime is detailed. Future directions for junction gated transistors are outlined.

Photocurrent amplification in Au/SiO2/n-6H-SiC MOS structures with a tunnel-thin insulator

The first observation of amplification of the photogeneration current in Au/SiO2/n-6H-SiC structures with a tunnel-thin insulator is reported. This effect can be used to increase the efficiency of existing UV-range 6H-SiC-based photodiodes. It also shows that bipolar SiC transistors with a MOS tunnel emitter can be produced.

Experimental and Simulated Results of SiC Microwave Power MESFETs

A variety of RF and microwave electronic devices can be fabricated from SiC. These SiC-based devices have many properties that make them near ideal for high temperature, high frequency, high power, and radiation hard applications. Progress in SiC bulk and epitaxial layer growth has been rapid in recent years and corresponding progress has been achieved in device fabrication and contact technology. Both 6H- and 4H-SiC substrates are commercially available, and high quality epitaxial layers can be grown. Prototype SiC electronic devices with very good DC and RF performance have been demonstrated and devices such as diodes are commercially available, while RF and high frequency transistors are rapidly approaching the commercialization state. In particular, SiC transistors such as MESFETs (MEtal Semiconductor Field-Effect Transistors) and SITs (Static Induction Transistors) with excellent DC and RF performance have been demonstrated and these devices are being developed for microwave power amplifier and oscillator applications. One of the most promising devices for microwave power applications is the MESFET. In this work the performance of microwave SiC MESFETs is investigated with a simulator that contains a physically based device model. The simulator permits the operation of the device to be examined and optimum device structures to be determined. This, in turn, permits performance capability and limitations to be investigated. The results of the simulations are compared to experimental measurements where possible, and excellent agreement between the simulated and measured data are obtained.

Silicon carbide FETs for high temperature nuclear environments

SiC transistors can operate at very high temperatures and survive very high radiation doses. These characteristics make SiC potentially the ideal technology for nuclear power applications. In this paper we report, for the first time, on the active in-core irradiation of 6H-SiC depletion-mode junction field-effect transistors (IFETs) at 25/spl deg/ and 300/spl deg/C in a nuclear reactor operated at 200 kW. No significant degradation in the device characteristics was observed until the total neutron fluence exceeded 10/sup 15/ n/cm/sup 2/ for irradiation at 25/spl deg/C, and no significant changes were observed even at 5/spl times/10/sup 15/ n/cm/sup 2/ at 300/spl deg/C. The results of this experiment may also indicate exciting evidence for the anneal of neutron displacement damage for devices irradiated at 300/spl deg/C.

Large-band-gap SiC, III-V nitride, and II-VI ZnSe-based semiconductor device technologies

In the past several years, research in each of the wide-band-gap semiconductors, SiC, GaN, and ZnSe, has led to major advances which now make them viable for device applications. The merits of each contender for high-temperature electronics and short-wavelength optical applications are compared. The outstanding thermal and chemical stability of SiC and GaN should enable them to operate at high temperatures and in hostile environments, and also make them attractive for high-power operation. The present advanced stage of development of SiC substrates and metal-oxide-semiconductor technology makes SiC the leading contender for high-temperature and high-power applications if ohmic contacts and interface-state densities can be further improved. GaN, despite fundamentally superior electronic properties and better ohmic contact resistances, must overcome the lack of an ideal substrate material and a relatively advanced SiC infrastructure in order to compete in electronics applications. Prototype transistors have been fabricated from both SiC and GaN, and the microwave characteristics and high-temperature performance of SiC transistors have been studied. For optical emitters and detectors, ZnSe, SiC, and GaN all have demonstrated operation in the green, blue, or ultraviolet (UV) spectra. Blue SiC light-emitting diodes (LEDs) have been on the market for several years, joined recently by UV and blue GaN-based LEDs. These products should find wide use in full color display and other technologies. Promising prototype UV photodetectors have been fabricated from both SiC and GaN. In laser development, ZnSe leads the way with more sophisticated designs having further improved performance being rapidly demonstrated. If the low damage threshold of ZnSe continues to limit practical laser applications, GaN appears poised to become the semiconductor of choice for short-wavelength lasers in optical memory and other applications. For further development of these materials to be realized, doping densities (especially p type) and ohmic contact technologies have to be improved. Economies of scale need to be realized through the development of larger SiC substrates. Improved substrate materials, ideally GaN itself, need to be aggressively pursued to further develop the GaN-based material system and enable the fabrication of lasers. ZnSe material quality is already outstanding and now researchers must focus their attention on addressing the short lifetimes of ZnSe-based lasers to determine whether the material is sufficiently durable for practical laser applications. The problems related to these three wide-band-gap semiconductor systems have moved away from materials science toward the device arena, where their technological development can rapidly be brought to maturity.