» WBG Devices • SiC diode • SiC MESFET • SiC MOSFET • SiC SIT • GaN HEMT • The group  » InP HEMT  » HBV Diode  » HEB  » Ferroelectrics  » MMIC  » Modelling  » High Speed Electronics		MEL » Research » Wide Band Gap Devices » SiC diode A SiC-diode can dissipate higher power than GaAs and Si due to the higher maximum temperature, it can also block higher voltage in the reverse direction. As a consequence, SiC-diodes can be used in microwave mixers and other switching applications where high power handling and linarity is of utmost importance. At MEL, we have fabricated microwave Schottky diodes and developed a single balanced mixers as a circuit demonstrator. The mixer achieved a third order input intercept point IIP3 of 31 dBm at 3 GHz, and a conversion loss of less than 7 dB which, to our knowledge, is state-of-the-art. The diode layer profile is shown in the figure. SiC diodes for microwave applications The first SiC component made at MEL was the microwave Schottky diode. This work was a part of Joakim Ericsson's thesis subject. Inspired by the work of Neudeck et al who made a high-level mixer based on a SiC-diode we decided to make a Schottky diode based on 4H-SiC that could perform even better. A theory for the optimization of the epilayer structure was developed and diodes were fabricated. Diodes were then used in a single balanced high level mixer to prove that superior intermodulation properties could be achieved. Motivation Due to the high breakdown field of SiC, a SiC Schottky diode can achieve a higher breakdown voltage compared to GaAs and Si-diodes assuming similar geometries and doping profiles. In addition, it can dissipate more power due to the higher operating temperature and the higher heatconductivity. This implies that a SiC-diode can be used in applications with higher powers. Possible applications are high level microwave mixers for very high linearity clampling diodes for dc-dc converters receiver protection circuits high power microwave mixers rugged noise diodes operation at elevated temperatures Device demonstrator Diodes based on a highly conducting substrate were investigated and optimized for high frequency performance. Following epilayer structure was used in our design. A matrix of our diodes are shown by the photo below. Following figure shows the calculated cut-off frequency versus donor concentration of the n-epi layer assuming a diode radius of 1, 2, 5, 10, 25, and 50 um. The maximum reverse voltage is 50V. The Schootky contact are made of Ti with a Au overlayer. The backside contact is Ni annealed at 950 C. The backside contact is electroplated with Au after annealing in order to facilitate soldering. Diodes with 50 um achieved a seriesresistance of 1.4 ohm, the ideality factor is 1.08 and the barrier height as determined from C-V measurements is 1.08 eV. Circuit demonstrator A single balanced mixer was designed based on a Spice model for the diode. The parameters were extracted from measurements. The figure below shows the block diagram for the mixer. The center frequency is 2 GHz. The photo shows the completed mixer. It was realized on teflon substrate. The simulated minimum conversion loss was 6 dB. The following diagrams shows the conversion loss versus frequency and LO-power. The highest IIP3 figure obtained is 31 dBm. No special attempts were made to optimize this number. Conclusions A new SiC Schottky process was developed and SiC Schottky microwave diodes were fabricated for the first time. Microwave diodes were designed and optimized, a Spice model was extracted The diodes were used in a single balanced high level mixer demonstrator Impressive IIP3 figures were obtained 31 dBm at PLO=30 dBm, and 28 dBm at PLO=25 dBm, to our knowledge the highest IIP3 value reported in literature for this type of mixer SiC diode roadmap at MEL The work on SiC diodes continues with Schottky diodes on semiinsulating substrate. Both the anode and the cathode are then accessible from the top and the diode can easily be contacted by wire bonding.

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