Martin Hoeferkamp,UNM

3D Sensor Characterization,Electrode Capacitance Measurements

Martin Hoeferkamp, Sally Seidel, Igor GorelovUniversity of New Mexico

8th RD50 Workshop, Prague27 June 2006

Martin Hoeferkamp,UNM2

Introduction

• Motivation: a need for 3D sensors to have an electrode capacitance compatible in value with existing front end chip requirements.

• Eg. , ATLAS Pixel detector upgrade, 3D sensors on TOTEM experiment will use ATLAS front end chip.

• Measured values on the order of 100fF, difficult with LCR meter• An alternative method of capacitance measurement is presented.

• 3D sensors received from Sherwood Parker (Hawaii U.) and Chris Kenney (Stanford U.) include:- non-irradiated sensor- irradiated 3D sensors– 2x1014 cm-2 55 MeV proton– 1x1015 cm-2 55 MeV proton

Martin Hoeferkamp,UNM3

3D Sensor Configuration• Configuration of Measured Devices

– Alternating columns of n- and p-electrodes– Most electrodes are connected together along each column– Some electrodes are left isolated, to be contacted and measured individually

• Top view layout • Layout dimensions( not same as ATLAS pixel)

Martin Hoeferkamp,UNM4

Electrode Capacitance, direct meas.• Direct Measurement uses standard CV measurement with LCR meter (HP4284A)

• Irrad 1015 55MeVp: N Electrode • Non-irradiated: N Electrode

• Irrad 2x1014 55MeVp: N ElectrodeResult: very low electrode capacitanceCnon-irrad N ~ 59fF(10KHz), 38fF(100KHz),

32fF(1MHz)Cirrad 2x1014 N ~ 72fF(10KHz), 72fF(100KHz),

62fF(1MHz)Cirrad 1x1015 N ~ 91fF(10KHz), 80fF(100KHz),

60fF(1MHz)

Martin Hoeferkamp,UNM5

Electrode Capacitance, direct meas.• Direct Measurement using LCR meter (HP4284A)

• Irradiated 1015 55MeVp: P Electrode • Non-irradiated: P Electrode

• Irradiated 2x1014 55MeVp: P Electrode

Result: very low electrode capacitanceCnon-irrad P ~ 71fF(10KHz), 58fF(100KHz),

46fF(1MHz)Cirrad 2x1014 P ~ 96fF(10KHz), 69fF(100KHz),

53fF(1MHz)Cirrad 1x1015 P ~ 98fF(10KHz), 70fF(100KHz),

55fF(1MHz)

Martin Hoeferkamp,UNM6

Electrode Capacitance, direct meas.• Direct Measurement using LCR meter (HP4284A)• Non-irradiated: N Electrode

Result: electrode capacitance decreases with lower temperature, and reaches a minimum value at ~ -10oC.

Martin Hoeferkamp,UNM7

Electrode Capacitance, direct meas.• Dependence of CV characteristics on measurement frequency

• The frequency dependence is observed at every temperature.

• Frequency dependence of irradiated sensors is due to the finite reaction time of the deep traps which respond better to lower frequency signals (Lancaster U.).

• The capacitances are higher for more heavily irradiated sensors

• There is a temperature dependence of the capacitance at a fixed measurement frequency.

• Capacitance depends on the frequency and the temperature, same as for planar sensors.

Martin Hoeferkamp,UNM8

Electrode Capacitance, indirect meas.

• Indirect Measurement using Decay Time of IR pulse on an isolated electrode.• Electrode is grounded through input impedance of a Picoprobe 35.• The IR laser induced charge is collected, rising signal on measured pulse.• When the laser is turned off the signal decay follows an exponential with a time

constant = R*(C+C3D) , referred to here as RC time constant.

• C3D is extracted from the decay time constant using values of probe resistance and capacitance.

PICOPROBE 35

R=1.25M

C=.05pF

To Oscilloscope

Pulsed1064nm IR Laser +Vbias

Gnd

Martin Hoeferkamp,UNM9

Electrode Capacitance, indirect meas.

• Laser: 1064 nm EG&G• Probes: Picoprobe 35 26GHz BW, Cascade Microtech coaxial• Oscilloscope: Tektronix TDS7254 2.5Ghz BW• Thermal Chuck: Micromanipulator (-60oC )

Vbias

PICOPROBE 35

R=1.25M

C=.05pF

Fast Pulser

OscilloscopeFocused Laser1064nm

Thermal Chuck

Martin Hoeferkamp,UNM10

Electrode Capacitance, indirect meas.• Indirect Measurement using Decay Time Picoprobe 35 signal, Non-irradiated p-electrode

Non-irradiated 3D PElectrode Decay, PP 35 Decay

0

0.05

0.1

0.15

0.2

0.E+00 1.E-07 2.E-07 3.E-07 4.E-07 5.E-07 6.E-07 7.E-07 8.E-07

Time (Sec)

Pu

lse

He

igh

t (A

U)

• RC Time Const = R*(C+C3d)= 169nS

• C3D = 85fF

Non-irradiated 3D PElectrode Decay, PP 35 Decay

y = 0.393995e-5939838.327796x

R2 = 0.9974080.001

0.01

0.1

1

0.E+00 1.E-07 2.E-07 3.E-07 4.E-07 5.E-07 6.E-07 7.E-07 8.E-07

Time (Sec)

Pu

lse

Hei

gh

t (A

U)

Martin Hoeferkamp,UNM11

Electrode Capacitance, indirect meas.• Indirect Measurement using Decay Time of signal on Picoprobe,• Non-irradiated p-electrode• Average RC time constant is 169nS, p-electrode capacitance is 85fF

Decay Curves, 3D sensor Non-irradiated

00.020.040.060.08

0.10.120.140.160.18

0.2

0.E+00 2.E-07 4.E-07 6.E-07 8.E-07

Bias Voltage (V)

Pu

lse

he

igh

t (A

U)

60V,tau=173nS

50V,tau=174nS

40V,tau=172nS

30V,tau=171nS

20V,tau=168nS

15V,tau=167nS

12V,tau=164nS

10V,tau=165nS

8V,tau=157nS

6V,tau=149nS

2V,tau=132nS

0V,tau=316nS

Capacitance, Non-irradiated 3D sensor

0

20

40

60

80

100

0 10 20 30 40 50 60

Bias Voltage (V)

Ca

pa

cit

an

ce

(fF

)

Martin Hoeferkamp,UNM12

Electrode Capacitance, indirect meas.• Indirect Measurement using Decay Time of signal on Picoprobe 35, Irradiated sensor p-electrode

Irradiated 2x1014 cm-2 55MeVp, 3D P Electrode

-0.01

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.00 200.00 400.00 600.00 800.00 1000.00

Time (nS)

Pu

lse

He

igh

t (m

V)

* On irradiated sensors there is a long tail at longer times which may be due to release of charge from traps produced by irradiation.

• Assuming a single dominant trapping time constant :

V = [Vo-Vo(RC/-RC)]e-t/RC + Vo(RC/-RC)]e-t

(Ref: S. Parker and C. Kenney, IEEE Trans. Nuc. Sci. ,Vol. 48, No. 5, Oct. 2001)

Irradiated 2x1014 cm-2 55MeVp, PP35 Decay

y = 0.09042668e-0.00490353x

R2 = 0.98572507

0.001

0.01

0.1

0.00 200.00 400.00 600.00 800.00 1000.00

Time (nS)

Pu

lse

He

igh

t (m

V)

Martin Hoeferkamp,UNM13

Electrode Capacitance, indirect meas.• Indirect Measurement using Decay Time of signal on Picoprobe 35, Irradiated sensor p-electrode

Time Const=R*(C+C3d)=177nS,C3D=91.6fF Second time const = 273nS

Irradiated 2x1014 cm-2 55MeVp, PP35 Decay

y = 0.11378952e-0.00565837x

R2 = 0.99611865

0.001

0.01

0.1

0.00 100.00 200.00 300.00 400.00 500.00 600.00

Time (mS)

Pu

lse

He

igh

t (m

V)

Irradiated 2x1014 cm-2 55MeVp, PP35 Decay

y = 0.03901790e-0.00359994x

R2 = 0.99303441

0.001

0.01

0.1

500.00 550.00 600.00 650.00 700.00 750.00 800.00 850.00

Time (nS)

Pu

lse

He

igh

t (m

V)

Irradiated 2x1014 cm-2 55MeVp, 3D P Electrode

-0.01

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.00 200.00 400.00 600.00 800.00 1000.00

Time (nS)

Pu

lse

He

igh

t (m

V)

Irradiated 2x1014 cm-2 55MeVp, PP35 Decay

y = 0.09042668e-0.00490353x

R2 = 0.98572507

0.001

0.01

0.1

0.00 200.00 400.00 600.00 800.00 1000.00

Time (nS)

Pu

lse

He

igh

t (m

V)

Martin Hoeferkamp,UNM14

Electrode Capacitance, indirect meas.

• Indirect Measurement using Decay Time of signal on Picoprobe• Irradiated 2x1014 cm-2 55MeVp sensor p-electrode• Average RC time constant is 177nS, p-electrode capacitance is 91.6fF• Second (trapping?) time constant is 273nS

Decay Curves, 3D sensor irrad 2x1014 55MeVp

0

0.05

0.1

0.15

0.2

0.25

0.E+00 1.E-07 2.E-07 3.E-07 4.E-07 5.E-07

Time (S)

Pu

lse

he

igh

t (A

U)

100V, tau=177nS

90V,tau=176.5nS

80V,tau=177nS

70V,tau=177nS

60V,tau=177.4nS

50V,tau=183.5nS

40V,tau=198nS

30V,tau=198nS

20V,tau=207nS

10V,tau=231nS

0V,tau=252nS

Capacitance, 3d Irrad 2x1014 cm-2 55MeVp

020406080

100120140160180

0 20 40 60 80 100

Bias Voltage (V)C

apac

itan

ce (

fF)

Martin Hoeferkamp,UNM15

Electrode Capacitance, indirect meas.• Indirect Measurement using Decay Time of signal on Picoprobe• Irradiated 1x1015 cm-2 55MeVp sensor p-electrode• Average RC time constant is 247nS, p-electrode capacitance is 147fF• Second (trapping?) time constant is 373nS

Capacitance, 3d Irrad 1x1015 cm-2 55MeVp

0

50

100

150

200

250

0 20 40 60 80 100 120

Bias Voltage (V)

Cap

acit

ance

(fF

)

Decay Curves, 3D sensor Irrad 1x1015cm-2 55MeVp

00.005

0.010.015

0.020.025

0.030.035

0.040.045

0.05

0.E+00 1.E-07 2.E-07 3.E-07 4.E-07

Bias Voltage (V)

Pu

lse

he

igh

t (A

U)

130V,tau=249.5nS

120V,tau=250nS

110V,tau=252nS

100V,tau=247nS

90Vtau=245nS

80V,tau=248nS

70V,tau=242nS

60V,tau=211nS

50V,tau=240nS

30V,tau=240nS

20V,tau=218nS

10V,tau=220nS

Martin Hoeferkamp,UNM16

Electrode Capacitance, calculation

• 3D Electrostatic Calculation (IES Coulomb):– P Electrode Length = 120 um– P Electrode Diameter = 20 um– Center electrode to nearest neighbors

Result: 3D calculation C3D P electrode = 31fFNote: result verified by S. Watts (Brunel U.) using an alternative calculation.

n n

n n

p p p

Martin Hoeferkamp,UNM17

Comparison of Results• Summary: Indirect measurement gives similar results to 10KHz LCR meter result

  Non-Irrad Irrad 2x1014 Irrad 1x1015

LCR meter 10KHz, P electrode 71 fF 96 fF 98 fF

LCR meter 100KHz, P electrode 58 fF 69 fF 70 fF

LCR meter 1MHz, P electrode 46 fF 53 fF 55 fF

Indirect Measurement, P electrode 85 fF 92 fF 147 fF

3D calculation, P electrode 31 fF  

Martin Hoeferkamp,UNM18

Summary• Two methods for measuring 3D sensor capacitance and results are

presented.

• In general the indirect method gives similar results to the direct method with the LCR meter frequency of 10KHz. This is also consistent with the RD50 guideline of 10KHz LCR measurements.

• 3D sensor Electrode Capacitance depends on frequency of the LCR meter and on the sensor temperature, same as for planar sensors.

• Need to further investigate possibility of extracting the trapping time constant from the second time constant of the irradiated sensors.