Tritium:Tritium: AA MicroPowerMicroPower SourceSource forfor OnOn--ChipChip ApplicationsApplications Nazir P. Kherani1, Baojun Liu2, Stefan Zukotynski1, Kevin P. Chen2 1Department of Electrical & Computer Engineering 2Department of Electrical and Computer Engineering and Department of Materials Science & Engineering University of Pittsburgh, Pittsburgh, PA, 15261 University of Toronto, Toronto, Ontario, M5S 3G4 Invited Presentation at Materials Innovations in an Emerging Hydrogen Economy February 24-27, 2008, Cocoa Beach, Florida Organized by the American Ceramic Society and ASM International Endorsed by National Hydrogen Association and Society for Advancement of Material and Process Engineering 1 OutlineOutline z Tritium: Basics z Tritium: A MicroPower Source – Beta-Voltaics – Beta-Powered MEMS – Beta-Luminescence – Cold Electron Source z Tritium: A Characterization/Diagnostic Tool – Tritium Tracer Studies – Tritium Effusion Studies – Defect Dynamics – Particle Sensor Applications z Summary 2 TritiumTritium z Isotope of Hydrogen 3 3 + − z H Æ He + β + νe + 18.6 keV z Nuclear Half-life: t ½ = 12.32 years λ = 1.78 x 10-9 s-1 z Activities: 1 Ci = 3.7 x 1010 Bq 1 Ci = 0.39 std cc 1 Ci = 33.7 μW z Biological: Half-life: 10 days ALI*: 80 mCi *Annual Limit on Intake z Chemically: Identical to 1H Mass effect (~3amu) Beta catalysis z Range (max): 4.5 – 6 mm in air 5 – 7 micron in water 3 ProducersProducers && UsersUsers CANDU z Producers of Tritium – Ontario Power Generation (OPG) • ~1 kg/year – Korean Electric Power Company (KEPCO) – USA • 225 kg produced since 1955 Tritium Producing Burnable Absorber Rods • 12-75 kg stockpiled (TPBARs) (Lithium Rods in a Light Water Reactor) – Russia – India, Pakistan Tritium Lighting z Users of Tritium – Pharmaceutical Research (~100g) – Tritium Lighting Industry (~30g) – Fusion Studies • Magnetic Confinement (ITER ~40g) • Inertial Confinement – Other Tritium in Natural Waterways 1 Tritium Unit (TU) = 1 T : 1018 H 4 OutlineOutline z Tritium: Basics z Tritium: A MicroPower Source – Beta-Voltaics – Beta-Powered MEMS – Beta-Luminescence – Cold Electron Source z Tritium: A Characterization/Diagnostic Tool – Tritium Tracer Studies – Tritium Outgassing & Effusion Studies – Defect Dynamics – Particle Sensor Applications z Summary 5 BetaVoltaicsBetaVoltaics electrons z 1951, Ehrenberg, Lang, & West: – Electron-voltaic effect (on a Se device) Sr90-Y90 z 1956, Rappaport – First direct conversion betavoltaic device (planar configuration, 0.4% efficiency) Si pn junction z 1968, Klein – Band-gap dependence of electron-hole pair (ehp) generation by ionizing radiation z 1974, Olsen – Theoretical treatment of betavoltaic conversion efficiencies for a variety of semiconductor materials z 1970s, D W Douglas Laboratories – Planar silicon betavoltaics fueled with 147Pm – Efficiencies ranged in 0.7 to 2% 6 RenewedRenewed InterestInterest inin RadioisotopeRadioisotope BatteriesBatteries z Continual miniaturization of electronic and electromechanical systems – Decreased power consumption z Integrated Power Sources (SoC) z High energy densities compared to chemical batteries z Operation in extreme environments – For example, temperatures of -100 to +150 oC 7 MicroPowerMicroPower ApplicationsApplications Sensor/Memory Chips SoC Microsystem Power requirement: 1-10 μW Power requirement: 1-10 mW Chip-scale Non-volatile Memory atomic clock RF-ID tag Micro-gas Analyzer Electrostatic actuation Chip-scale of MEMS/NEMS Navigation system 8 MarketMarket z All Batteries: $50 billion z Target markets for betavoltaic batteries – Oil, gas, and environmental – Military – Medical – Space – Emerging MEMS/NEMS z Market for betavoltaics $1 billion + 9 Electron/BetaElectron/Beta VoltaicsVoltaics Depletion Region Metal Contact + -- Band Diagram + + -- + + -- + _ ehp Energetic + -- + Electrons + + n-Si + -- p-Si _ + V I ehp: electron-hole pair 10 ChoiceChoice ofof RadioisotopeRadioisotope Isotope Eavg Emax P Work T1/2 (keV) (keV) (W/g) (kWh/ (yrs) 4y/g) H-3 5.7 18.6 0.34 10.3 12.3 Ni-63 21 66 0.07 2.5 92 Sr-90 540 900 0.75 25 28 Pm-147 62 230 0.34 7.3 2.6 Tritium z Low energy β- emitter (benign radioisotope) z Low cost: $2.5-$4/Ci z Long enough lifetime z Can be immobilized in a solid matrix z On-chip integration z Mature (existing tritium lighting industry) 11 Intrinsic Tritiated Amorphous Silicon Betavoltaic Device z Substitute tritium for hydrogen in Tritiated hydrogenated amorphous silicon pin Intrinsic Layer (uniform) photovoltaic devices p-a-Si:H z Tritium within the energy conversion layer i-a-Si:H:T – In contrast to betas originating from a source external to the device n-a-Si:H z Volume source battery – Attained through stacking of many cells – In contrast to a planar surface source battery Kherani, Kosteski, Gaspari, Zukotynski, Shmayda,, Fusion Technol. 28, (1995) 1609-1614. 12 aa--Si:TSi:T BetavoltaicBetavoltaic DeviceDevice At t ~ 0 At t ~ 10 days Tritiated Isc = 0.98 nA Isc < 0.1 nA Intrinsic Layer (uniform) V = 21 mV oc p-a-Si:H η = 0.1% i-a-Si:H:T n-a-Si:H p-a-Si:H i-a-Si:H:T n-a-Si:H Tritiated Delta Layer Kosteski, Kherani, Stradins, Gaspari, Shmayda, Sidhu, Zukotynski, IEE Proc. Circuits Devices Syst. 150, No.4, (2003) 27-281. 13 aa--SiHSiH BetavoltaicBetavoltaic CellCell PoweredPowered byby TT2 GasGas a-SiH Betavoltaics At t ~ 0 At t ~ 46 days 2 with ultrathin contact Isc = 637 nA/cm η < 0.1% Voc = 457 mV Cr, 5nm η = 1.2% p-a-Si:H, 20 nm i-a-Si:H, 450 nm, 10-15 % H n-a-Si:H SS substrate Tritium gas pressure: 678 torr Deus, 28th PVSEC, 2000. 14 PorousPorous SiliconSilicon 3D3D BetavoltaicsBetavoltaics z Introduce micropores in silicon through electrochemical anodization z Create pn junction in the pores through diffusion of n-type dopant z Introduce an appropriate radionuclide in the pores z A Volume Source Battery Gadeken, Sun, Kherani, Fauchet, Hirschman, US Patent 7250323 (2007). 15 3D3D VersusVersus 2D2D BetavoltaicsBetavoltaics η2D = 0.02% η3D = 0.2% Sun, Kherani, Hirschman, Gadeken, Fauchet, Adv Mater 17 (2005) 1230-1233. 16 IIIIII--VV BetavoltaicsBetavoltaics AlGaAs/GaAs Heterojunction Source of Generate Open Output Efficiency betas d current circuit Power, (%) Betavoltaics density Voltage, μW/cm2 μA/cm2 V Tritium- 0.04 0.75 0.024 5.6 titanium Tritium 0.76 0.91 0.55 5.8 gas Tritium 0.12 0.78 0.074 --- green lamp Andreev, Kavetsky, Kalinovsky, Larionov, Rumyantsev, th Shvarts, Yakimova, Ustinov, 28 PVSEC, 2000. 17 SiliconSilicon CarbideCarbide BetavoltaicsBetavoltaics 4H SiC BV Cell 4H SiC pin BV Cell 1 mCi, 63Ni Source (66keV) 8.5 GBq, 33P Source (249 keV) 2 I = 2.1 μA/cm2 Isc = 16.8 nA/cm sc V = 2.04 V Voc = 0.72 V oc η = 6% η = 4.5% Ni/Au Ni p SiC n SiC, 0.25 μm, 7Ndoped p SiC, 4 μm i SiC n SiC p+ SiC Ni/Au Al/Ti Chandrashekhar, Thomas, Li, Spencer, Lal, Eiting, Krishnamoorthy, Rodgers, George, Robertson, Appl. Phys. Lett., 88 (2006) 033506 Brockman, Appl. Phys. Lett., 88 (2006) 064101. 18 ContactContact PotentialPotential DifferenceDifference BetavoltaicsBetavoltaics Αir-medium CPD BV Solid CPD BV 2 2 Ιsc = 2.7 nA/cm Ιsc = 5.3 nA/cm Voc = 0.5 V Voc = 0.16 V 10 0.6 5 0.4 0 0.2 -5 0.0 0.1 mm darkness Current (nA) Current (nA) -0.2 -10 0.3 mm betavoltaic 0.6 mm -0.4 -15 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 -0.1 0.0 0.1 0.2 Voltage (volts) Voltage (volts) Liu, Chen, Kherani, Zukotynski, Antoniazzi, Appl. Phys. Lett., 92 (2008). 19 MEMS: Radioisotope-Powered Piezoelectric Generator z Self-reciprocating direct-charging cantilever z Direct conversion of collected- charge-to-motion energy into electrical – Radioisotope kinetic energy stored in the cantilever – Piezoelectric generator converts stored mechanical energy into electrical energy z Overall efficiency 2.78% Lal, Duggirala, Li, IEEE Pervasive Computing, 4, (2005), pp. 53-61. 20 BetaLuminescenceBetaLuminescence z 1898, Becquerel Becquerel – Radioluminescence – Phosphorescence material: potassium uranyl sulphate z 1920s, Elster, Geitel, and Cookers – Alpha radiation induced scintillations in ZnS. radiation phosphor z 1967, International Atomic Energy Agency (IAEA) – Standards for the use of common RL sources. hν – Most common: tritium beta-luminescence z Present – Tritium gas lighting – Radium ZnS:Cu paint – Novel materials & technologies in Betaluminescence • Organic - all-organic formulation: polystyrene and fluorescent dye electrons - organic system with inorganic phosphor • Inorganic - semiconductor pn junctions - incorporation of tritium in solid matrix: amorphous materials, hydrides, carbon nanotubes, zeolites hν 21 ColdCold ElectronElectron SourceSource z Tritium immobilized in a solid z Materials – Tritiated metal tritides – Tritiated amorphous silicon • Plasma enhanced chemical vapour deposition: entire film • Tritiation post film deposition: ~50 nm – Tritiated silica on Si-chip • High pressure tritium loading • Laser irradiated locked tritium – Tritiated silicon • High pressure tritium loading • Surface region: ~ 10 nm – Tritiated carbon nanotubes 22 OutlineOutline z Tritium: Basics z Tritium: A MicroPower Source – Beta-Voltaics – Beta-Powered MEMS – Beta-Luminescence – Cold Electron Source z Tritium: A Characterization/Diagnostic Tool – Tritium Tracer Studies – Tritium Outgassing & Effusion Studies – Defect Dynamics – Particle Sensor Applications z Summary 23 TritiumTritium TracerTracer TechniqueTechnique • Tritium as a tracer in measurement of hydrogen permeation in polymer for selection of new material in hydrogen fuel cell. • Two diagnostics to trace permeating HT: an ionization chamber tritium detector and an HTO water trap/copper oxide furnace/HTO water