M.A. Carvajal, F. Simancas, D. Guirado, J. Banqueri, S. Martínez-García, A.M. Lallena and A.J. Palma

EVALUATION OF DMOS TRANSISTORS AS ELECTRON

BEAMS DOSIMETER

Introduction DMOS study

Methods and materials Results and discussion Conclusion DMOS study

CD 4007 characterization Thermal characterization Characterization as dosimeter Results and discussion

Conclusions Acknowledgements

Summary

Complementary technique applied just after the cancer extraction.

Electron beams provided by a LINAC. Aims to destroy the remaining tumoral cells on the edge of

the cancer. Only one session.

Introduction

Intra Operative Radiotherapy (IORT):

IORT:

Introduction

Treatment planning in IORT:

Introduction

Software using MonteCarlo code

Dosimetry control very suitable

MOSFETs dosimeters provides immediate readout

Dosimetric system:

Materials and Methods

Commercial pMOS transistors (non RADFETs) Reader unit and dosimeters based on commercial

pMOSFET developed by our research group Thermal characterization need for thermal

compensation Readout techniques for linearity and resolution

improvements

7

Measurement method: Two currents: Linear range improvement

Three currents: Thermal compensation (IZTC)

1

2

121

1I

I

VVVV SSSt

ZTC

ZTCSSZTCSt

I

I

VVVV

2

,02

,

1

C

ZTCSSCSS

II

IIVVVV

2

222

02

Non thermal compensated

Materials and Methods

8

Method And Materials:Block diagram of dosimetric

system

Sensor module

S

G

D

B

pMOSJFET

RG

ADC

ADC

DACI2C

ID

JFETcontrol

FT232

USB

0

1 1 3 A

4 5 6 B

7 8 9 C

. D

2Readerunit

Reader unitUniv.Granada

EEPROMmemory

BJT

555

MCU

I.A.

Dosimetric system:

Method And Materials

Method And Materials:Experimental setup

Model DMOS tested (Unbiased mode): BS250F, ZVP3306 and ZVP4525

Four transistors per model Irradiated by a Siemens Mevatron KDS:

6 MV electrons Field 25x25 cm2 At the iso-center, 100 cm Normal incidence

Method And Materials:Thermal characterization

I-V characteristics at different temperatures Extracted by a semiconductor analyzer

(B1500, Agilent Technologies) Temperature variations produced by a

climate chamber (VCL4006 Vötosch Industryetedhnik, Germany)

The IZTC was not found for the studied DMOS transistor:

T1 (ZVP3306)

0.0E+00

4.0E-04

8.0E-04

1.2E-03

1.6E-03

2.0E-03

2 2.5 3 3.5V (V)

I (A

)

-15.1-4.8-0.99.720.030.540.549.7

Method And Materials:Thermal characterization

No IZTC then 2 currents algorithm to determine the VT.

Numerical compensation: Determination the thermal coefficient of VT (VT)

ZVP3306

y = -0.0027x + 2.1138R2 = 0.9962

1.98

2.00

2.02

2.04

2.06

2.08

10 20 30 40 50T (ºC)

|VT|(

V)

Method And Materials:Thermal characterization

Thermal compensation

Thermal coefficients:

Table 2.TV

(mV/ºC) for different DMOS

Average BS250F -2.24 0.18

ZVP3306 -2.48 0.16

ZVP4525 -3.3 0.4

Method And Materials:Thermal characterization

Results and discussion

ZVP3306

y = 3.4151xR2 = 0.9993

y = 3.5845xR2 = 0.9983

y = 3.5447xR2 = 0.9985

y = 3.5739xR2 = 0.998

0

50

100

150

200

250

0 10 20 30 40 50 60D (Gy)

|V

T| (

mV

)

82 87 93 98

Accumulate VT shift as dose function

Results and discussion

ZVP3306

2.5

2.9

3.3

3.7

4.1

4.5

0 10 20 30 40 50 60D (Gy)

Sen

(m

V/G

y)

82 87 93 98

Accumulate VT shift as dose function

Average sensitivities:

Results and discussion

Table 2. Sensitivity (mV/Gy)

Average ZVP3306 3.71 0.27

BS250F 3.14 0.37

ZVP4525 3.38 0.44

ZVP3306: Thermal coefficient: (-2.48 ± 0.16) mV/ºC Average sensitivity: (3.7 ± 0.3) mV/Gy Then, thermal drift: (0.60 ± 0.07) Gy/ºC

Results and discussion

Conclusions of DMOS study

ZVP3306 presented the highest sensitivity and lowest dispersion

However, the thermal dependence is too high to be used as dosimetry control in IORT.

A thermal compensation algorithm is needed or the sensitivity must be increased (for example using an external bias voltage)

To look for new dosimeter candidates: We have tested the CD4007 integrated circuit.

Texas Instruments (USA) 0.3 € and 100 nm of SiO2

New pMOS as dosimeter:Characterization of CD 4007

CHARACTERIZATION CD 4007:Thermal response, IZTC

T2

0.0E+00

5.0E-05

1.0E-04

1.5E-04

2.0E-04

2.5E-04

3.0E-04

1.8 1.9 2 2.1 2.2 2.3 2.4 2.5VDS(V)

I(A)

15º20º25º30º35º40º45º

I-V of five in saturation region, VGD =0 f from 15 to 45ºC

ID

VS

VDD

VT thermal coefficient: (-2.0 ± 0.3) mV/ºC

Thermal compensation is needed. IZTC found for CD4007: (137 ± 19) A

Three current algorithm can be applied

CHARACTERIZATION CD4007:Thermal response, IZTC

T1

y = -2.2E-03x + 6.4E-02

y = -1.7E-06x - 1.6E-03

-0.06

-0.04

-0.02

0

0.02

0.04

10 20 30 40 50T (ºC)

VT (

V)

UncompensatedCompensated

CmV

CmV

To

T

V

V

/º)24.01.0(

/º)3.00.2(

Five transistor studied:

CHARACTERIZATION CD4007:Irradiation conditions

Buildup (1.5 cm, and only for photon beams)

Ionization chamber PTW23332

CD4007 dosimeter modules (At the isocentre)

CHARACTERIZATION CD 4007:Linearity, Photon beams 6 MV

y = 5.2778xR2 = 0.9999

y = 5.3057xR2 = 0.9995

y = 5.1321xR2 = 0.9997

y = 5.1778xR2 = 0.9996

y = 5.2968xR2 = 0.9995

0

20

40

60

80

100

120

140

0 5 10 15 20 25 30

D (Gy)

VT (

mV

)

7

8

9

10

11

12

CHARACTERIZATION CD 4007:Sensitivity, Photon beams 6 MV

4.5

4.7

4.9

5.1

5.3

5.5

5.7

0.0 5.0 10.0 15.0 20.0 25.0 30.0D (Gy)

Sen

(m

V/G

y)

7 8 9 10 11 12

CHARACTERIZATION CD 4007:Sensitivity, Photon beams 6 MV

Transitor Value Uncertainty7 5.278 0.0138 5.297 0.0229 5.30 0.02

10 5.132 0.01911 5.311 0.01812 5.306 0.018

Avg 5.27 0.07

Sen (mV/Gy)

CHARACTERIZATION CD 4007:Linearity, Electron beams 6 MV

y = 4.5959x

R2 = 0.9998

y = 4.5761x

R2 = 0.9995

y = 4.6387x

R2 = 0.9997

y = 4.4938x

R2 = 0.9993

y = 4.5667x

R2 = 0.9998

0

20

40

60

80

100

0 5 10 15 20

D (Gy)

VT (

mV

)

1

2

3

4

5

4.2

4.3

4.4

4.5

4.6

4.7

4.8

0.0 5.0 10.0 15.0 20.0D (Gy)

Sen

(m

V/G

y)

1 2 3 4 5

CHARACTERIZATION CD 4007:Sensitivity, Electron beam 6 MV

CHARACTERIZATION CD 4007:Sensitivity, Electron beam 6 MV

Transitor Value Uncertainty1 4.596 0.0122 4.576 0.0203 4.494 0.0234 4.639 0.0175 4.567 0.0126 4.865 0.012

Avg 4.62 0.13

Sen (mV/Gy)

CHARACTERIZATION CD 4007:Thermal considerations

Value UncertaintyNon compensated -2.0 0.3

Compensated -0.01 0.24Photons 6 MV 5.27 0.07Electrons 6 MV 4.62 0.13

Non compensated Photons 6 MV -0.39 0.12Dose coefficient (Gy/ºC) Electrons 6 MV -0.44 0.05

Compensated Photons 6 MV -2.E-03 5.E-02Dose coefficient (Gy/ºC) Electrons 6 MV -3.E-03 5.E-02

Thermal drift (mV/ºC)

Sensitivity (mV/Gy)

Conclusions of CD4007

CD4007 presents a sensitivity of radiation of

(4.62 ± 0.13) mV/Gy for photon beams of 6 MV Thermal dose coefficient of 5 cGy/ºC A good candidate to be use as IORT dosimeter Need to study in depth thermal dependence, linearity

and calibrations Possible sensitivity increasing: biasing, stacking pMOS

transistors.

Acknowledgements

University Hospital San Cecilio (Granada, Spain). For funding this work: Ministerio de Ciencia e

Innovacion and the Junta de Andalucía. And partially supported by European Regional

Development Funds (ERDF)

M.A. Carvajal, F. Simancas, D. Guirado, J. Banqueri, S. Martínez-García, A.M. Lallena and A.J. Palma

Thank you very munch for your attention

carvajal@ugr.es