高功率电子学第5章开关技术solid state switchpcss

1、Photoconductive Semiconductor Switching and ApplicationsJames Dickens, Center for Pulsed Power & Power Electronics, Texas Tech UniversityLubbock, TX, USASemiconductor device where light controls the flow of current.PIN or Bulk switch structureLinear or Non-linear conduction2Photoconductive SwitchesP

2、hotoconductive SwitchesAdvantagesExtremely compactNegligible jitterFast rise-timeDisadvantagesSingle devices not suitable for MV rangesMaterial limitationsChange in conductivity of a material with light.When light is absorbed, charge carriers are generated, increasing conductivity.4Photoconductivity

3、5Extrinsic Photoconduction Intrinsic photoconduction, direct band to band transition. Extrinsic photoconduction, defect to band transition.Ideal CharacteristicsInfinite resistance in the off stateZero resistance in the on stateShort transition time6Photoconductive SwitchesThe charge carrier generati

4、ng rate by photon8Switch GeometriesLateral GeometryVertical GeometryModes of Operation Linear mode Laser pulse controls switch opening and closing Laser energy requirement can be prohibitively large Non-Linear Avalanche mode High gain, switch closed until external current removed Lock On (GaAs) Coll

5、ective impact ionization 电源电压较低电脉冲与光脉冲同步Tp (光脉冲宽度)Tr（载流子复合特征时间）The linear mode is characterized by one electron hole pair produced for each photon absorbed. Therefore, the conductivity of the material is, to the first order, linearly proportional to the total photon flux illuminating the semiconduct

6、or material, and the switch conductivity approximately follows the shape of the optical drive pulse. The switch closes as the optical intensity increases, remains closed while illuminated, and opens with a characteristic time constant related to the carrier lifetimes after the optical pulse is remov

7、ed.Linear modeThe conductivity of a semiconductor is defined as:where q = charge of an electron, n/p is the electron/hole mobility, n/p is theelectron/hole concentration. The resistance is related to the conductivity by:where L is the current path length, and A is the cross sectional area.Finally, t

8、he on state resistance is calculated as:where no is the net carrier concentration.11Off State ResistanceIn the on state, the carrier concentration is:where is the photon flux and is the bination lifetime.Assuming a constant light source, the photon flux is related to the intensity of the light sourc

9、e through the relation:Accounting for the absorbed and reflected light, the intensity es:12On State ResistanceThe on state carrier concentration es:Substituting and simplifying, the on state resistance is calculated:13On State Resistance简单计算On State Resistance上式是针对本征电导，对于非本征电导，要做以下修正OperationAuthorM

10、aterialGeometryRoff OhmsRon OhmsEmax kV/cmTrigger Energy JDogan4H-SiCLateral1.E+1220101500Zhu4H-SiCLateral, Circular1.E+0911550.06Sullivan6H-SiCVertical1.E+11111061300Kelkar6H-SiCVertical1.E+111.523011000Sheng3C-SiCLateral, Fingers1.E+0645250120000LeFurSiLateral1.E+043021.410ZutavernGaAsLateralVarie

11、d14342.5TTU4H-SiCVertical1.E+09111601500Summary of Past PCSS Work GaAs PCSS have been extensively researched at Sandia National Labs for over 15 years At moderate electric fields ( 10 kV/cm), switches operate in non-linear regime (filamentary conduction).GaAs PCSSNon-liner mode非线性模式所需光能比线性模式小3个数量级PC

12、SS存在响应延迟，一般开关导通滞后于光脉冲ns量级电流上升速度快，达到ps量级，远小于光脉冲上升时间自由载流子浓度大，内部存在类似雪崩倍增的过程Lock-on效应，开关导通后，只要提供足够能量，即使光脉冲消失，仍能保持导通状态，并且内部电场锁定在一个只与开关材料有关的常数丝状电流 Current filaments form at moderate fields, reducing lifetime of switch by degrading contactGaAs Filaments Images of photoluminescence from localized bination,

13、initiation energy as low as 200 nJ Integrated bar LD stack triggers multiple filaments Shares current, improves switch life Filament forms at each LD lineGaAs PCSSA. Mar, et. al., “FIRESET APPLICATIONS OF IMPROVED LONGEVITY OPTICALLY ACTIVATED GaAs PHOTOCONDUCTIVE SEMICONDUCTOR SWITCHES,” 2001Pulsed

14、 Power Conference, 2001. Filament width scales with current Switch Life: 1.0 kA: 466 shots 2.5 kA: 58 shots 3.0 kA: 25 shotsGaAs PCSSA. Mar, et. al., “FIRESET APPLICATIONS OF IMPROVED LONGEVITY OPTICALLY ACTIVATED GaAs PHOTOCONDUCTIVE SEMICONDUCTOR SWITCHES,” 2001Pulsed Power Conference, 2001.GaAs P

15、CSS Contact DamageA. Mar, et. al., “DOPED CONTACTS FOR HIGH-LONGEVITY OPTICALLY ACTIVATED, HIGH GAIN GaAs PHOTOCONDUCTIVE SEMICONDUCTOR SWITCHES” 1999 Pulsed Power Conference, 1999.Non-linear GaAs PCSS Transition from linear (6 kV) to lock-on (10 kV)J. Yuan, et. al., “Peculiar Photoconductivity in N

16、onlinear GaAs Photoconductive Semiconductor Switch,” 2009 Pulsed Power Conference, 2009.Field Dependent Operation Lock-on (10 kV) to non-linear regime ( 10 kV)J. Yuan, et. al., “Peculiar Photoconductivity in Nonlinear GaAs Photoconductive Semiconductor Switch,” 2009 Pulsed Power Conference, 2009.GaA

17、s Trigger Generators GaAs switches up to 50 kV, 7 kA with 10 mJ at 1064 nm Switches last 50 100s of total shots at these levels before complete switch failure Long lifetime ( 1E7 shots), low initiation energy ( J) only at low current ( 5 A) Useful for trigger generators, LD drivers Need new material

18、 for high current, voltage, and switch lifetime.GaAs PCSS Summary GaAs PCSS have been primary focus up until recently More recent work has switched to SiC, mostly due improved breakdown strength for high voltage switchingSwitch Materials Advantages: High resistivity substrates (1E9 1E12 -cm) Breakdo

19、wn field ( 3 MV/cm) Thermal Conductivity ( 4x silicon) Disadvantages: Material Defects micropipes, basal plane dislocations Limited Availability few manufacturers Difficult to process high temperature stable, implantation depth limited, low temperature p-type dopingSilicon Carbide29ON State Resistan

20、ce versus Energy4H-SiC PCSS4H-SiC was chosen as a replacement to 6HHigh-purity, semi-insulating (HPSI) substrates availableHigher mobility and carrier lifetimesComparable dielectric strength and thermal conductivityCompensating defects within the bandgap available for extrinsic excitation4H-SiC PCSS

21、 Design All prototype switches fabricated in-house Vertical switch designed to minimize on-state resistance Hollow electrode allows illumination semi-transparent contactsExperimental ResultsMinimum on-state resistance achieved 11 Peak photocurrent of 14 A into 25 loadExperimental ResultsExperimental

22、 ResultsMotivationDecrease ON-state resistanceReduce laser energy requirementReduce Switch LengthLateral - Vertical Geometry Increase bination LifetimeMeasure carrier lifetime (MWPCD)Compare relative conductivitySwitch InnovationsExperimental Results4HV1 Gridded NiSi Contact4HV2 ITO/Ni Contact4HV3 N

23、iSi/ITO Contact4HV4 Gridded Contact with Increased LifetimeSiC PCSS Summary4H-SiC superior1E9 resistance change from OFF-ON stateGeometry & Lifetime improvements reduce laser requirements and improve switch performanceHigh voltage (50 kV) vertical switches are possiblePCSS ApplicationsCompact Pulsed

24、 PowerHF pulse generation (UWB,HPM)High voltage trigger generatorsRadiation (UV, X-Ray, THz) detectorsCompact Pulsed PowerPCSS-based stacked blumlein pulserW. Nunnally, et. al., 6H SILICON CARBIDE PHOTOCONDUCTIVE SWITCHES FOR HIGH POWER APPLICATIONS, 2006.PCSS-BASED TRIGGER FOR MANY SWITCHESPCSS-BAS

25、ED TRIGGER FOR MANY SWITCHESUWB GenerationTwo GaAs PCSS used to generate bipolar UWB pulseC. Baum, L. Carin, A. Stone, Ultra-wideband short pulse electromagnetics, pp 20-22, 1996.UWB GenerationCurrent (A)C. Baum, L. Carin, A. Stone, Ultra-wideband short pulse electromagnetics, pp 20-22, 1996.UWB Gen

26、erationHigh gain GaAs PCSS triggered by 82 MHz Femto-second laserW. Ji, W. Shi, ULTRA-WIDEBAND MICROWAVE GENERATION BASED ON GAAS PHOTOCONDUCTIVE SEMICONDUCTOR SWITCHES, (unknown publish date).Pulse GenerationRadiated SignalOther ApplicationsFrozen waveform generatorsDC to RF conversion for microwav

27、e generationHigh power short pulse applications, eg, wideband radarGaAs PCSS X-Ray DetectionGaAs PCSS demonstrated 30 ps response.J Rauch, et. al., “GaAs A VERSATILE PHOTOCONDUCTIVE MATERIAL FOR THE MEASUREMENT OF X-RAYS IN PULSED POWER APPLICATIONS,” 2005 Pulsed Power Conference, 2005.Other Applica

28、tionsDiamond Radiation DetectorsRadiation hardened high energy detectorsDetects UV, Gamma rays, X-rays, and other high energy particlesUsed for detecting nuclear effects, high intensity x-ray, andneutron sourcesOther ApplicationsTerahertz Pulse GenerationWideband PCSS antennasAntennas fabricated by

29、depositing shaped electrodes onto bulk materialLarge number of applications ranging from bioscience to security screeningP Kirawanich, “A Full Wave Analysis of a Terahertz-Pulse Generation for Wide-bandgap Photoconductive Antennas using a Field-carrier Transport Scheme,” proceedings Int. Conf. ., 2009.Ot