Extraction of Effective Carrier Velocity and Observation of ... - JSTS

JOURNAL OF SEMICONDUCTOR TECHNOLOGY AND SCIENCE, VOL.8, NO.2, JUNE, 2008 117Q i[ fC ]Q i[ fC ]40353025201510504540353025201510501st term in equation2nd term in equationchannel chargeV GS- V TH= 0.6 VV DS= 1.0 VNMOS0 100 200 300 400 500V GS-V TH= -0.6 VV DS= -1.0 VPMOSL poly[ nm ]1st term in equation2nd term in equationchannel charge0 100 200 300 400 500L poly[ nm ]Fig. 5. Channel charge obtained from equation (1) of NMOSand PMOS.constant value. However, this formalism begins to breakdown when the carrier travel distance is scaled down.The average carrier velocity can be substantially greaterthan that expected. In other words, as the longitudinalelectric field increases, the electron gas starts to be indisequilibrium with the lattice. There is an insufficientnumber of phonon-scattering events experienced by theelectron during its flight with the result that electrons canbe accelerated to velocities higher than the saturationvelocity, thus approaching ballistic transport conditions.Extracted effective velocity of electrons and holes areplotted in Fig. 6 (a) and (b) as a function of L poly and1/L poly . The linear dependence on 1/L poly is observedespecially short channel regime. It should be noted theobtained v eff of electrons under L poly of 57 nm exceeds10 7 cm/s, indicating that the velocity overshoot isobserved. And we predict larger electron velocity asdevice dimensions continue to decrease. On the otherhand, no hole velocity overshoot is observed even at 37nm channel length. The different trend for the ratio ofmobility and velocity between electrons and holes isshown in Fig. 7. In contrast to the similar rates ofmobility and velocity in long channel device, there is aElectron velocity [ X10 7 cm/s ]Hole velocity [ x10 7 cm/s ]1.41.21.00.80.60.40.20.00.400.350.300.250.200.150.100.050.001/L poly[ nm -1 ]0.000 0.005 0.010 0.015 0.020 0.025 0.03NMOSV GS - V TH = 0.6 VV DS = 1.0 V0 100 200 300 400 500L poly [ nm ](a)1/L poly[ nm -1 ]0.000 0.005 0.010 0.015 0.020 0.025 0.0300.450 100 200 300 400 500L poly [ nm ](b)PMOSV GS - V TH = -0.6 VV DS = -1.0 VFig. 6. Effective carrier velocity as a function of L poly , 1/L poly .μ n/ μ p5432100 100 200 300 400 500L poly[ nm ]V ds= 1.0 VV ds= 0.5 VV ds= 0.1 VV ds= 0.01 V|V gs-V th|= 0.6 VFig. 7. The difference rate of mobility and velocity betweenelectrons and holes.disparity between mobility and velocity in short channeldevice. This is probably due to the smaller portion ofgradual-channel region in short-channel MOSFETs andalso easier generation of hot carriers in NMOSFETs. Fig.8 shows v eff as a function of V ds for devices with L effranging from 36 to 500 nm. It is observed that theeffective carrier velocity tends to saturate at long channeldevice and p-MOSFETs, although electron velocity543210v eff,n/ v eff,p

118 JUNSOO KIM et al : EXTRACTION OF EFFECTIVE CARRIER VELOCITY AND OBSERVATION OF …Carrier velocity [ x10 7 cm/s ]1.41.21.00.80.60.40.2|V gs-V th| = 0.6 VPMOSL poly= 37 nmL poly= 56 nmL poly= 180 nmL poly= 500 nmL poly= 36 nmL poly= 57 nmL poly= 180 nmL poly= 500 nmNMOS0.0-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0V DS[ V ]Fig. 8. Effective carrier velocity according to the drain bias inNMOS and PMOS.overshoot occurs when the gate length is shorter than 60nm.IV. CONCLUSIONSThe electron velocity overshoot is observed while nohole velocity overshoot is observed down to 37 nmchannel length at room temperature. This indicates morefrequent scattering and heavier effective mass of holescompared with electrons. And as the longitudinal electricfield increases, there is an insufficient number ofphonon-scattering events experienced by the electronduring flight with the result that electrons can beaccelerated to velocities higher than the saturationvelocity, thus approaching ballistic transport conditions.ACKNOWLEDGMENTSThis work was supported Samsung Electronics Ltd.and Nano Systems Institute.REFERENCES[1] J. B. Rldan, F. Gamiz, J. A. Lopez-Villanueva, andJ. E. Carceller, “Modeling effects of electronvelocityovershoot in a MOSFET,” IEEE Transactionson Electron Devices, vol. 44, no. 5, pp. 841-846,May 1997.[2] F. Assad, Z. Ren, D. Vasileska, S. Datta, and M.Lundstrom, ”On the performance limits for SiMOSFET’s : a theoretical study,” IEEE Transactionson Electron Devices, vol. 47, no. 1, pp. 232-240,Jan. 2000.[3] J. Wang, and M. Lundstrom, “Ballistic transport inhigh electron mobility transistors,” IEEE Transactionson Electron Devices, vol. 50, no. 7, pp. 1604-1609,July 2003.[4] J. Kim, J. Lee, Y. Yun, B-G. Park, J. D. Lee, andH. Shin, “Accurate extraction of mobility, effectivechannel length, and source/drain resistance in 60nm MOSFETs,” International Conference on SolidState Devices Materials, pp. 442-443, 2007.[5] Y. Yun, I. M. Kang, B-G. Park, J. D. Lee, and H.Shin, “Extraction of effective carrier velocity inRF MOSFET,” Topical Meeting on Silicon MonolithicIntegrated Circuits in RF Systems, pp. 72-75, Jan.10-12, 2007.[6] A. Lochtefeld, and D. A. Antoniadis, “On experimentaldetermination of carrier velocity in deeply scaledNMOS : How close to the thermal limit?,” IEEEElectron Device Letters, vol. 22, no. 2, pp. 95-97,Feb. 2001.[7] F. Assaderaghi, P. K. Ko, and C. Hu, “Observationof velocity overshoot in silicon inversion layers,”IEEE Electron Device Letters, vol . 14, no. 10, pp.484-486, Oct. 1993.[8] T. Mizuno and R Ohba, “Experimental study ofcarrier velocity overshoot in sub-0.1 μm devices -Physical Limitation of MOS structures-,” TechnicalDigest of IEDM, pp. 109-112, 1996.[9] Ritesh Gupta, Sandeep Kumar Aggarwal, MridulaGupta, and R. S. Gupta, “Short channel analyticalmodel for high electron mobility transistor toobtain higher cut-off frequency maintaining reliabilityof the device,” Journal of Semiconductor Technologyand Science, vol. 7, no. 2, June, 2007.[10] S. Lee, “A new method to extract carrier velocityin sub-0.1- μm MOSFETs using RF measurements,”IEEE Transactions on Nanotechnology, vol. 5, no.3, pp. 163-166, May 2006.

JOURNAL OF SEMICONDUCTOR TECHNOLOGY AND SCIENCE, VOL.8, NO.2, JUNE, 2008 119Junsoo Kim was born in Korea onJuly 13, 1980. He received B.S.degree in electronic engineering fromKyunghee University, Gyunggi-do,Korea, in 2003. He is currentlypursuing the Ph.D. degree in SeoulNational University, Seoul, Korea.His major interest is deep submicrometer device modelingand characterization issues.Jaehong Lee was born in Korea onOctober 25, 1983. He received B.S.degree in electrical engineering andcomputer science from Seoul NationalUniversity, Seoul, Korea, in 2006,where he is currently working towardthe Ph.D. degree. His major interestis deep submicrometer device modeling and characterizationissues.Yeonam Yoon received the B.S.,M.S. degrees in electrical engineeringand computer science from SeoulNational University, Seoul, Korea, in2004, 2008, respectively. In 2008 hejoined Samsung Electronics Company,Ltd., Gyunggi-do, Korea, His majorinterest is deep submicrometer device modeling andcharacterization issues.Byung-Gook Park received the B.S.and M.S. degrees in electronicsengineering from Seoul NationalUniversity, Seoul, Korea, in 1982and 1984, respectively, and the Ph.D.degree in electrical engineering fromStanford University, Stanford, CA, in1990. From 1990 to 1993, he was with AT&T BellLaboratories, Murray Hill, NJ, where he contributed tothe development of 0.1-μm CMOS and its characterization.From 1993 to 1994, he was with Texas Instruments,Dallas, TX, developing 0.25-μm CMOS. In 1994, hejoined the School of Electrical Engineering, SeoulNational University, as an assistant professor. He iscurrently a full professor. He has been in charge of theresearch of Inter-university Semiconductor ResearchCenter (ISRC) in Seoul National University since 2003as the chief of the research department. His currentresearch interests are nanoscale CMOS devices, Sisingle-electron devices, nonvolatile memory devices,and organic electroluminescent displays. Dr. Park was amember of the International Electron Devices MeetingSubcommittee on Solid State Devices from 2001 to 2002and worked for Silicon Nanoelectronics Workshop 2005as a program chair.Jong Duk Lee was born in Youngchun,Kyungpook, Korea. He received theB.S. degree in physics from SeoulNational University in 1966. Hereceived the Ph.D. degree from theDepartment of Physics at the Universityof North Carolina at Chapel Hill in1975. He served at the Military Communication Schoolas a ROTC officer from 1966 to 1968. He then worked atthe Engineering College of Seoul National University asa teaching assistant in the Department of AppliedPhysics until 1970. He was an Assistant Professor in theDepartment of Electronics Engineering at KyungpookNational University from 1975 to 1978. In 1978, hestudied microelectric technology in HP-ICL at Palo Alto,CA, USA, and soon afterward worked for the KoreaInstitute of Electronic Technology (KIET) as the directorof the semiconductor division. He established the KIETKumi Facility and introduced the first polysilicon gatetechnology in Korea by developing 4K SRAM, 32K and64K Mask ROM's, and one-chip 8-bit microcomputer.In July 1983, he moved to the Department of ElectronicsEngineering of Seoul National University, which hasbeen merged to School of Electrical Engineering in 1992,where he is now a Professor. He started to establish theInter-University Semiconductor Research Center (ISRC)in 1985, and served as the director from 1987 to 1989.He served as the chairman of the Electronics EngineeringDepartment from 1994 to 1996. He worked for SamsungSDI Co., Ltd. as the Head of Display R&D Center for ayear on the leave of SNU in 1996. He was the member ofthe steering committee for IVMC(International Vacuum

120 JUNSOO KIM et al : EXTRACTION OF EFFECTIVE CARRIER VELOCITY AND OBSERVATION OF …Microelectronics Conference) from 1997-2001 and KCS(Korean Conference on Semiconductors) from 1998-2008. He was the conference chairman of IVMC´97 andKCS´98 who led the IVMC´97 and the KCS´98successfully. He was also the member of IEDM(InternationalElectron Devices Meeting) Subcommittee on Detectors,Sensors and Displays operated by IEEE Electron DevicesSociety from 1998 to 1999, he has been elected to thefirst president of the Korean Information Display Societyin June 1999 to serve until Dec.31,2001. He concentratedhis study on the image sensors such as Vidicon type,MOS type, and also CCD to help Samsung SDI Co. andSamsung Electronics Co. since 1985. His current researchinterests include sub 0.1 um CMOS structure and technology,CMOS image sensors and FED(Field Emission Display),and organic LEDs and TFTs. He published more than221 papers in the journals such as IEEE-ED and EDL,Journal of Vacuum Science and Technology, AppliedPhysics and Journal of Electrochemical Society, including160 SCI journal papers. He presented more than 361papers including 213 international conference papers. Healso registered 12 US, 4 Japanese, and 28 Korean patents.Now he is a member of IEEE, ECS, AVS, SID, KPS,KVS, IEEK, and KSS.Hyungcheol Shin received the B.S.(magna cum laude) and M.S. degreein electronics engineering from SeoulNational University, Seoul Korea, in1985 and 1987, respectively, and thePh. D. degree in electrical engineeringfrom the University of California, Berkeley, in 1993.From 1994 to 1996, he was with Motorola AdvancedCustom Technologies, as a Senior Device Engineer. In1996, he joined the Department of EECS, KAIST,Daejeon, Korea, in 1996 as an Assistant Professor.During his sabbatical leave from 2001 to 2002, he waswith Berkana Wireless, CA, as a Staff Scientist in chargeof CMOS RF modeling. In 2003, he joined the School ofElectrical Engineering and Computer Science, SeoulNational University, Seoul, as an Associate Professor. Hiscurrent research interests include RF circuits, CMOS RFmodeling, CIS, and nano CMOS. He has published over300 technical papers in international journals andconference proceedings and also wrote chapters in aJapanese book on plasma charging damage and semiconductordevice physics. Prof. Shin was a committee memberInternational Electron Devices Meeting. He also has servedas a committee member of several international conferences,including International Workshop on Compact Modeling(IWCM) and as a committee member of IEEE EDSGraduate Student Fellowship. He is a Lifetime Memberof the Institute of Electronics Engineers of Korea (IEEK)and received the Second Best Paper Award from theAmerican Vacuum Society in 1991. He also received theExcellent Teaching Award from the Department of EECSat KAIST in 1998 and from Seoul National University in2005. In 1999, he received The Haedong Paper Awardfrom the Institute of Electronics Engineers of Korea(IEEK). He is listed in Who’s Who in the World.