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High Voltage Multiplexing for ATLAS Tracker Upgrade EG Villani on behalf of the ATLAS HV group

High Voltage Multiplexing for ATLAS Tracker Upgrade EG Villani on behalf of the ATLAS HV group. STFC Rutherford Appleton Laboratory. Outlook. I ntroduction: ATLAS Upgrade HV mux needs HV project description: devices and control circuitry Summary & conclusions. 1.

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High Voltage Multiplexing for ATLAS Tracker Upgrade EG Villani on behalf of the ATLAS HV group

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  1. High Voltage Multiplexing forATLAS Tracker UpgradeEG Villani on behalf of the ATLAS HV group STFC Rutherford Appleton Laboratory

  2. Outlook • Introduction: ATLAS Upgrade HV mux needs • HV project description: devices and control circuitry • Summary & conclusions 1

  3. ATLAS Phase II Tracker Upgrade 2

  4. ATLAS Phase II Tracker Upgrade • Phase 2 (HL-LHC) • Replacement of the present Transition • Radiation Tracker (TRT) and Silicon • Tracker (SCT) with an all-silicon • strip tracker Conceptual Tracker Layout • Challenges facing HL-LHC silicon detector upgrades • Higher Occupancies ( 150 interactions / bunch crossing) • Finer Segmentation • Higher Particle Fluences ( 1014outmost layers to  1016 innermost layers • Increased Radiation Tolerance ( 10increase in dose w.r.t. ATLAS ) • Larger Area (~200 m2) • Cheaper Sensors • More Channels • Efficient power/bias distribution / low material budget Short Strip (2.4 cm) -strips (stereo layers): Long Strip (4.8 cm) -strips (stereo layers): r = 38, 50, 62 cm r = 74, 100 cm From 1E33 cm-2 s-1 …to 5E34 cm-2 s-1 3

  5. The Stave concept andHV distribution in ATLAS Upgrade • Designed to reduce radiation length • Minimize material by shortening cooling path • 48 Modules glued directly to a stave core with embedded pipes • Designed for mass production • Simplified build procedure • Minimize specialist components • Minimize cost ~ 1.2 meters Carbon fibre facing Stave Cross-section Bus cable A Stavelet is a shortened stave prototype with up to four modules on each side, used for preliminary tests, including power distribution Carbon honeycomb or foam Coolant tube structure Hybrids 4

  6. HV distribution in ATLAS Upgrade • The ‘ideal’ solution would be one HV bias line for each sensor: • High Redundancy; • Individual enabling or disabling of sensors and current monitoring; • But the increased number of sensors in the Upgraded Tracker implies a trade off among material budget, complexity of power distribution and number of HV bias lines. • Use single (or more) HV line to power all 12 sensors in a ½ stave and use one HV switch under DCS control for each sensor to disable malfunctioning detectors. 5

  7. HV distribution in ATLAS Upgrade • DC Reference Approach • Each Sensor sees a different bias voltage (over-deplete top sensors in serial power chain by ~30V) • Current measuring circuit may be placed on each hybrid • Some mixing of HV and LV (DC) currents • AC Reference Approach • All detectors see same bias voltage • Current measuring circuit most naturally located on End-of-Stave Card • No mixing of HV and LV (DC) currents HV SW HV SW HV SW HV SW 6

  8. HV distribution in ATLAS Upgrade 7

  9. HV distribution in ATLAS Upgrade: devices • High Voltage switches requirements: • Must be rated to 600V (or more for pixels) plus a safety margin • Must be radiation hard (rules out most of Si based devices and optocouplers) • Off-state impedance Roff>> 1GΩ • On-state impedance Ron<< 1kΩ and Ion > 1mA • Must be non-magnetic (rules out electromechanical switches) • Must maintain satisfactory performance at -30 C • Must be small and cheap 8

  10. HV distribution in ATLAS Upgrade: devices • High Voltage switches considered: • Si based devices: • Bipolar transistors: main effect of radiation damage is lowering of gain and relatively high base current required • MOS transistors: high voltage power MOSFET usually have thick gate oxide that makes them not rad – hard ( possible exception – see later slides) • Si JFET: potentially rad – hard but hard - to - find • Non – Si based devices: • SiC based devices: on the market there are already examples of High Power rated devices SiC JFET (Semisouth) BJT (Fairchild/Transic), SiC SJT (Genesic) • GaN devices: (Transphorm, Panasonic, Infineon ) as for SiC devices there are switches operating at kV’s Materials Property Si SiC-4H GaN Band Gap (eV) 1.1 3.2 3.4 low leakage; higher displacement threshold (more rad-hard) Critical Field 1E6 V/cm .3 3 3.5 higher BV voltage/thinner; Electron Mobility (cm2/V-sec) 1450 900 2000 Electron Saturation Velocity (106 cm/sec) 10 22 25 higher current density; Thermal Conductivity (Watts/cm2 K) 1.5 5 1.3 easier cooling; 9

  11. HV distribution in ATLAS Upgrade: SiC device tests • Initial 4-switch box with SemiSouth SiC JFET SJEP170 with slow controlled circuitry was tested to switch a stavelet; no additional noise seen 10

  12. HV distribution in ATLAS Upgrade: SiC device tests Ids(A) Ids(pA) Pre irradiation Pre irradiation Post irradiation Post irradiation Vds(V) Vgs(V) • Semisouth SJEP170 JFET characterization tests • Pre and post irradiation tests results (>30Mrad gamma) 11

  13. HV distribution in ATLAS Upgrade: SiC device tests Beam profile Los Alamos Sep 2012 SemiSouth SJEP170 Run: Irradiation up to 5E14 1MeV n-eq 12

  14. HV distribution in ATLAS Upgrade: SiC device tests ID [A] ID [A] Fast pulse test: a (negligible) increase in on-state resistance is observed following irradiation 13

  15. HV distribution in ATLAS Upgrade: SiC device tests IG [pA] IS [pA] IG [pA] IS [pA] • Off-state leakage current preliminary test resultsvery good • Unfortunately, SemiSouth went out of business in 2012 14

  16. HV distribution in ATLAS Upgrade: Si device tests Si JFET 800 μm 800 μm • #4 Silicon High Voltage N JFETs 2N6449 devices mounted on a PCB, #3 bare dies JFETs of the same type and #3 PCB samples were irradiated to 1/3 1015 p/cm2 with 26 MeV protons (doses of around 1MGy in 10 minutes) at Birmingham University, UK • The JFETs mounted on PCB were previously characterized at RAL: for Vds = 250 V and Vgs = -9 V maximum Ids < 200 pA for the 4 devices tested • Onset of Breakdown at Vdg = 300 V, as per DS • The JFETs show an average DC resistance of 1.8kOhm @ [Vgs = 0 V, T = 22 C] • The bare dies JFETs were irradiated to study their gamma spectrum emission 15

  17. HV distribution in ATLAS Upgrade: Si device tests VGS(V) VGS(V) IGS(A) IDS(A) IDS(A) IGS(A) IDS(A) IDS(A) • Si JFET # 4 I - V curves: UNIRRADIATED IDS , IGS vs. VGS (left), IRRADIATED IDS , IGS vs. VGS (right)Maximum Idscompliance: 2 mAMaximum Igscompliance: 0.1 mAUNIRRADIATED Ids = 50 pA @ [VGS =-9 V Vds =250 V] IRRADIATED Ids = 37 nA @ [VGS =-11 V @ Vds =250 V] • Leakage current increases by around 3 o.f.m. (but so would leakage current of sensors); • Main issue is the increased Rdson ( kohm to  100’s khom) preventing their use as mA switches; • Interfet (manufacturer) potentially interested in fabricating P type JFET (which may be more rad – hard) 16

  18. HV MUX control scheme Negative HV multiplier To Detector HV JFETDEPL filter V source -HV • Regardless of the devices used as HV switches, a control circuitry, referenced to a high potential, to enable them is needed • An investigated option consists of an AC coupled control switch based upon a voltage multiplier (it works with depletion and enhancement mode devices depending on the polarity of the diodes ) 17

  19. HV MUX control scheme Negative HV multiplier To Detector HV JFET Average current consumption: 50 μA filter V source • The voltage needed is generated using a 2.5 V (or lower amplitude) square wave AC. Only the coupling capacitors from Vsrc need to be rated for HV. • The (in the example shown) negative voltage is generated ONLY when the JFET needs shutting off: no power is needed during normal operation (i.e. when the JFET switch is ON). 18

  20. HV MUX control scheme test fin= 50 kHz Vbias =0V fin= 100 kHz Vbias =0V fin= 50 kHz Vbias =-300V fin= 50 kHz Vbias =-300V Multimeter : Fluke 287Signal generator: Tektronix AFG3252HV PSU: EA-BS315-04B (#2 in series to get 300V) V MPY Vout (Meter) ‘MOBO’ ‘DABO’ connection Vin (Sign. Gen) (HV PSU) Voltage MPY * The voltage across R2 is measured vs. amplitude and frequency of Vin ( square wave, 50% duty cycle) and for Vhigh = [0, -300] V * Applying -300 V a slight decrease in abs(Vout) is noticed (some leakage current over the board surface is the likely cause) 19

  21. Conclusions • High Voltage distribution via HV switches and DCS control is being investigated • A number of devices, based upon Si and wider bandgap materials, are being investigated (Panasonic, Transphorm, Genesic, Cree, Interfet) but no final solution yet • The control circuitry to enable and disable the HV switches also being investigated. 20

  22. Backup slides • A cascodescheme allows using lower voltage devices to achieve high voltage switching • More components, more area required • Increased rdson I

  23. Backup slides Base current with 500 Ohm Base Series Resistor (Rc = 231k) Drain current with 500 Ohm Base Series Resistor (Rc = 231k) Some works on the SPICE model for the FSICBH057A120 SiC BJT, provided by Dave, will run some simulations with the control circuitry.* The Ib seems to be a little high for the control circuit as is, need some modifications to it (DGT, 2nd stage, cascode) II

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