High voltage multiplexing for atlas tracker upgrade eg villani on behalf of the atlas hv group
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High Voltage Multiplexing for ATLAS Tracker Upgrade EG Villani on behalf of the ATLAS HV group PowerPoint PPT Presentation


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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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High Voltage Multiplexing forATLAS Tracker UpgradeEG Villani on behalf of the ATLAS HV group

STFC Rutherford Appleton Laboratory


Outlook

  • Introduction: ATLAS Upgrade HV mux needs

  • HV project description: devices and control circuitry

  • Summary & conclusions

1


ATLAS Phase II Tracker Upgrade

2


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


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


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


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


HV distribution in ATLAS Upgrade

7


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


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) 1450900 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


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


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


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


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


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


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


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


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


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


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


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


Backup slides

  • A cascodescheme allows using lower voltage devices to achieve high voltage switching

  • More components, more area required

  • Increased rdson

I


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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