High Voltage Multiplexing forATLAS Tracker Upgrade

EG 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

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ATLAS Phase II Tracker Upgrade

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3

ATLAS Phase II Tracker Upgrade

Challenges facing HL-LHC silicon detector upgrades

•Higher Occupancies ( 150 interactions / bunch crossing)

⤷ Finer Segmentation•Higher Particle Fluences ( 1014 outmost layers to 1016 innermost layers

⤷ Increased Radiation Tolerance ( 10 increase in dose w.r.t. ATLAS )

•Larger Area (~200 m2)⤷ Cheaper Sensors

•More Channels⤷ Efficient power/bias distribution / low

material budget

Phase 2 (HL-LHC)Replacement of the present TransitionRadiation Tracker (TRT) and Silicon Tracker (SCT) with an all-silicon strip tracker

Conceptual Tracker Layout

Short Strip (2.4 cm) -strips (stereo layers):Long Strip (4.8 cm) -strips (stereo layers):

r = 38, 50, 62 cmr = 74, 100 cm

From 1E33 cm-2 s-1 …to 5E34 cm-2 s-1

The Stave concept andHV distribution in ATLAS Upgrade

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~ 1.2 meters

Bus cable

Hybrids Coolant tube structure

Carbon honeycomb or foam

Carbon fibre facing

Stave Cross-section

A Stavelet is a shortened stave prototype with up to four modules on each side, used for preliminary tests, including power distribution

• 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

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.

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HV distribution in ATLAS UpgradeDC 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

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HV SW

HV SW HV SW

HV SW

HV distribution in ATLAS Upgrade

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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

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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

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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;

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

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HV distribution in ATLAS Upgrade: SiC device tests

Semisouth SJEP170 JFET characterization tests• Pre and post irradiation tests results (>30Mrad gamma)

Vds(V)

Ids(pA)Ids(A)

Vgs(V)

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Post irradiation

Pre irradiation Pre irradiation

Post irradiation

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HV distribution in ATLAS Upgrade: SiC device tests

Los Alamos Sep 2012 SemiSouth SJEP170 Run: Irradiation up to 5E14 1MeV n-eq

Beam profile

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HV distribution in ATLAS Upgrade: SiC device tests

0.0E+00 5.0E-07 1.0E-06 1.5E-06 2.0E-060

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2 Pre Rad - 500ns Pulse ResponseID = 2AID = 1A

Time [s]0.0E+00 5.0E-07 1.0E-06 1.5E-06 2.0E-06

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2 Post Rad - 500ns Pulse ResponseID = 2AID = 1A

Time [s]

Fast pulse test: a (negligible) increase in on-state resistance is observed following irradiation

ID [A] ID [A]

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HV distribution in ATLAS Upgrade: SiC device tests

Off-state leakage current preliminary test results very good

• Unfortunately, SemiSouth went out of business in 2012

0 30 40 50 60 70 80 90 100 200 300 400 500 600 7000.0

0.1

1.0

10.0

100.0

1000.0

10000.0

1E+00

1E+01

1E+02

1E+03

1E+04

1E+05

1E+06

1E+07

1E+08Is1 Is2 Is3 Is4

Ig1 Ig2 Ig3 Ig4

0 30 40 50 60 70 80 90 100 200 300 400 500 600 7000.0

0.1

1.0

10.0

100.0

1000.0

10000.0

1E-01

1E+00

1E+01

1E+02

1E+03

1E+04

1E+05

1E+06

1E+07

1E+08Is1RAD Is2RAD Is3RAD Is4RAD

Ig1RAD Ig2RAD Ig3RAD Ig4RAD

IS [pA]IS [pA] IG [pA]IG [pA]

• #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

800 μm

800 μm15

Si JFET

HV distribution in ATLAS Upgrade: Si device tests

Si JFET # 4 I - V curves: UNIRRADIATED IDS , IGS vs. VGS (left), IRRADIATED IDS , IGS vs. VGS (right)Maximum Ids compliance: 2 mAMaximum Igs compliance: 0.1 mA UNIRRADIATED 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)

IDS(A) IDS(A)

IDS(A)VGS(V)

IGS(A)IDS(A)VGS(V)

IGS(A)

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HV distribution in ATLAS Upgrade: Si device tests

HV MUX control scheme

Negative HV multiplier

filter

HV JFETDEPL

V source

• 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 )

-HV

To Detector

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Negative HV multiplier

filterHV JFET

V source

Average current consumption: 50 μA

• The voltage needed is generated using a 2.5 V (or lower amplitude) square wave AC. Only the coupling capacitors from V src 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).

To Detector

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HV MUX control scheme

0

S VEXC

C 110n

C 210n C 18

100n

R 22Meg

R 1

5k

V h ig h300V dc

0

V M P Y

* 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)

‘DABO’ connection

Voltage MPY

‘MOBO’

1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

-30.0

-25.0

-20.0

-15.0

-10.0

-5.0

0.0Vbias=0V Vbias=-300Vfin=50KHz fin=100kHz fin=50KHz fin=100kHz

Vin(V) Vout(V) Vout(V) Vout(V) Vout(V)1.0 -4.41 -4.41 -3.91 -4.051.5 -7.05 -7.06 -6.37 -6.402.0 -9.76 -9.80 -8.90 -9.102.5 -12.49 -12.56 -11.50 -11.803.0 -15.22 -15.34 -14.00 -14.503.5 -17.97 -18.12 -16.40 -17.204.0 -20.72 -20.90 -18.95 -19.904.5 -23.47 -23.70 -21.50 -22.605.0 -26.23 -26.50 -24.10 -25.40

fin = 50 kHz Vbias =0V

fin = 100 kHz Vbias =0Vfin = 50 kHz Vbias =-300Vfin = 50 kHz Vbias =-300V

V MPY Vout

Vin

Multimeter : Fluke 287Signal generator: Tektronix AFG3252HV PSU: EA-BS315-04B (#2 in series to get 300V)

(HV PSU)(Sign. Gen)

(Meter)

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HV MUX control scheme test

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.

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I

Backup slides

C 1910p f

C 2010p

C 2110p

J 6

J F 2N 6449

R 112G iga

C 2210p

R 72G iga

R 82G iga

J 3

J F 2N 6449

R 92G iga

J 4

J F 2N 6449

J 5

J F 2N 6449

A cascode scheme allows using lower voltage devices to achieve high voltage switching• More components, more area required• Increased rdson

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)

Drain current with 500 Ohm Base Series Resistor (Rc = 231k) Base current with 500 Ohm Base Series Resistor (Rc = 231k)

II

Backup slides