108 IEEE ELECTRON DEVICELETTERS, VOL. 27, NO. 2, FEBRUARY 2006 Microwave p-i-n Diodes and Switches Based on 4H-SiC Nicolas Camara, Konstantinos Zekentes, Member, IEEE, Leonid P. Romanov, Aleksey V. Kirillov, Mykola S. Boltovets, Konstantin V. Vassilevski, Member, IEEE, and George Haddad, Life Fellow, IEEE Abstract—The 4H-SiC p-i-n diodes were designed, fabricated, and characterized for use in microwave applications. The diodes with mesa structure diameters betw een 80 and 150 m, exhib- ited a blocking voltage of 1100 V, a 100-mA differential resistance of 1–2 , a capacitance below 0.5 pF at a punchthrough voltage of 100 V and a carrier effective lifetime between 15–27 ns. X-band mi- crowave switches based on 4H-SiC p-i-n diodes are demonstrated for the first time. The switches exhibited insertion loss as low as 0.7 dB, isolation up to 25 dB and were able to handle microwave power up to 2.2 kW in isolation mode and up to 0.4 kW in insertion mode. Index Terms—Microwave switches, p-i-n diode, silicon carbide. I. INTRODUCTION T HE p-i-n diodes find wide usage in RF, UHF, and mi- crowave circuits. Switches, attenuators, modulators and phase shifters based on p-i-n diodes are used in wireless com- munication systems, radars, magnetic resonance imaging sys- tems, industrial heating etc. Most commercial p-i-n diodes are fabricated from Si and GaAs. Their technology is mature and thus, their performance in terms of power and switching speed is limited by the physical properties of these semiconductors. Indeed, the maximum switching power of a p-i-n diode is de- fined by two diode parameters: 1) the breakdown voltage and 2) the amount of power the diode is capable to dissipate. On the other hand, the switching speed is defined by the thickness of the base (i-layer) as well as to a lesser degree by carriers life- time and velocity. Hence, increasing the intrinsic layer thick- ness of the diodes in order to increase the switching power leads to a decrease of the switching speed. Equivalently, increasing Manuscript received August 31, 2005. This work was supported by the INTAS Foundation under Grant 01–603 and the NATO SfP Program under Grant SfP-978 011, and supported in part by the European Research Office of the U.S. Army under Grant N68171-02-M5465. The work at Newcastle University was supported by the EPSRC, U.K., under Grant GR/S20420/01 and Grant GR/R96385/01. The review of this letter was arranged by Editor K. T. Kornegay. N. Camara is with the MRG, IESL, Foundation for Research and Technology- Hellas, Crete 71110, Greece, and also with IMEP, ENSERG, Grenoble Cedex 1 FR-38016, France. K. Zekentes is with the MRG, IESL, Foundation for Research and Tech- nology-Hellas, Crete 71110, Greece (e-mail: trifili@physics.uoc.gr). L. P. Romanov and A. V. Kirillov are with the Svetlana-Electronpribor, St. Petersburg 194021, Russia. M. S. Boltovets is with the State Enterprise Research Institute “ORION,” Kiev 03057, Ukraine. K. V. Vassilevski is with the Department of Electrical, Electronic and Com- puter Engineering, University of Newcastle, Newcastle NE1 7RU, U.K. G. Haddad is with the Department of the Electrical Engineering and Com- puter Science, the University of Michigan, Ann Arbor, MI 48109-2122 USA. Digital Object Identifier 10.1109/LED.2005.862686 the switching speed for a given power level would require a de- crease of the i-layer thickness leading to a decrease of the power. Therefore, new semiconductors have to be used for the fabrica- tion of p-i-n diodes in order to increase the power handling and the switching speed. SiC has the physical properties for fabricating microwave p-i-n diodes outperforming their counterparts made from Si and GaAs. It has a higher avalanche breakdown field ( V/cm in 4H-SiC) and thus, a reverse biased SiC p-i-n diode, having the same intrinsic layer thickness and minority carrier lifetime as a Si p-i-n diode, can handle high frequency signals with times higher power. Moreover, SiC has a thermal conductivity about five times higher and may operate at temperatures at least four times higher than silicon. Therefore, a SiC p-i-n diode could dissipate about 20 times higher thermal power than a similar Si diode. In previous papers [1]–[3], we have demonstrated the suitability of 4H-SiC diodes for microwave applications on nonoptimized epitaxial structures with moderately n-doped diode base. In this letter, the development of microwave 4H-SiC p-i-n diodes on optimized device structure as well as the per- formance of X-band switches incorporating these diodes is reported. II. DIODE STRUCTURE AND FABRICATION Commercially available p-i-n structures (from the top 1 m, p cm m, n cm m, n cm ) grown on 4H-SiC, 8 off substrates, were used for the fab- rication of the diodes. Diode’s fabrication procedure was de- scribed elsewhere [4]–[6]. The diode dies of 0.6 0.6 mm were mounted in microwave packages. III. DC ELECTRICAL CHARACTERIZATION OF DIODES The current–voltage ( – ) curves of the packaged diodes measured at temperatures up to 700 C exhibited typical be- havior for 4H-SiC p-i-n diodes [6]. The breakdown voltage in air was V while in fluorinert a sharp knee characteristic of a bulk avalanche breakdown appeared at a bias around 1100 V. The forward differential resistance varies linearly with the inverse of the applied forward current up to 20 mA and then at a lower rate due probably to the decrease of the carrier effective lifetime at high injection levels (Fig. 1). The measured values of are lower than the expected one for the resistance of the base i-layer (13.4 for a 80 m mesa diameter diode) showing an effective conductivity modulation of this layer. 0741-3106/$20.00 © 2006 IEEE Authorized licensed use limited to: Newcastle University. Downloaded on July 09,2010 at 13:34:46 UTC from IEEE Xplore. Restrictions apply.