gamma radiation induced on teo2 thin film of dielectric properties

Gamma Radiation induced changes in the MOS Structure Aℓ/TeO2/n-Si

Under the Supervision of

Prof. S. L. Sharma

Venkateswarlu Somepalli

(09PH6004)

Contents

Introduction

Aim of the work

Experimental procedure

Result and discussion

Plots

Future work

References

Gamma ray is a packet (or photon) of electromagnetic radiation emitted from the

nucleus during radioactive decay which is form the most important primary cause of

the ionizing radiation hazard to the general population during most radiological

emergencies. One cannot see or feel any gamma radiation hitting one’s body.

Naturally, therefore, one needs quite specialized equipment for the detection of

gamma radiation .

Introduction

There are three important mechanisms of interaction by which gamma radiation

interact with the matter leading to the attenuation of gamma radiation which is most

important to understand the working of different gamma radiation detection

systems and for the realistic estimation of the level of radiation hazard. These

interaction mechanisms are photoelectric interaction, Compton interaction and the

interaction leading to pair production.

whenever a gamma ray photon interacts with the matter it generate a variety of

defects in the solid materials of all kinds and induces changes in the structural,

optical, electrical and other physical properties of the thin solid films.

The understanding of the changes in different physical properties of the thin solid

films due to the gamma radiation exposure is vital from the viewpoint of the

physics the materials as well as from the viewpoint of the design and development

of gamma radiation dosimeters and sensors.

A large number of efforts have been devoted in the recent past to investigate the

influence of gamma irradiation on the properties of the thin films of metal oxides

such as SnO2, In2O3, CeO2, NiO, TeO2, SiO, etc.

The study of the effects of ionizing radiation on the MOS devices (such as MOS

capacitors, MOSFETs, integrated circuits, etc.) has been an interesting area of

research due to their widespread applications in the field of radiation dosimetry

over the past several decades.

Aim of this work

To study the effect of gamma irradiation on the dielectric properties of thin TeO2

layers. In the present work, for the first time, a study has been carried out to

understand the nature and working of the MOS structure with an oxide layer of

tellurium dioxide (TeO2) and the effects of different levels of gamma radiation dose

on the working of this structure.

The study includes measurements on the capacitance-voltage (C-V) and

conductance-voltage (C-V) characteristics at a high frequency of 1 MHz using a HP

4192A LF impedance analyzer. From these measurements, the voltage and radiation

dose dependences of the real dielectric constant ,imaginary dielectric constant

,series resistance (Rs) and density of interface states (Dit) have been obtained for the

MOS structure, Aℓ/TeO2/n-Si for three thicknesses (namely, (100, 150 and 200 nm)

of the TeO2 layer.

Several samples of the MOS structure (Aℓ/TeO2/n-Si), for each of the three

thicknesses (100, 150 and 200 nm) of the TeO2 layer, were fabricated using n-type

(phosphorous doped) single crystal of silicon wafer of thickness 300 m and the wafer was chemically cleaned using the RCA cleaning procedure.

After cleaning of the surface, ohmic contact was made with aluminum on one side of

the wafer. Thickness of the ohmic contact was about 300 nm. On the backside of the

wafer, a thin layer of TeO2 was grown by thermal evaporation. On the top of the TeO2

layer, another aluminum ohmic contact was made. All the aluminum ohmic contacts

were prepared by thermal evaporation in a vacuum.

The capacitance-voltage (C-V) and conductance-voltage (G-V) measurements were

performed at high frequency of 1 MHz using a high precision (4192A LF) impedance

analyzer for the MOS structure before and after the gamma irradiation at different

levels of radiation dose. The gamma irradiation of the MOS structure was carried out

by source at room temperature. During this measurements, a test signal of an

amplitude of Vrms = 500 mV was used.

Experimental Procedure

Result and Discussion

Measured capacitance and measured conductance plots, as a function of gate

voltage before and after gamma irradiation at different dose levels for Al/TeO2/n-Si

MOS structures having three thickness of 100, 150 and 200 nm shows irradiation

dispersion in accumulation region which is shown in fig 1(a,b), 2(a,b) and 3(a,b)

respectively. In all cases it has been observed that the capacitance increases with

increase in irradiation dose and such behavior of this capacitance values are

attributed to particular distribution of surface states between TeO2/Si interfaces.

when gamma interact with metal oxide it produces the electron hole pair and

electron gets quickly disappears with metallic contact due to their high drift velocity

and leavings behinds the holes through out the metal oxide and interfacing region.

These holes increases the existing field in the interfacing region and results to increase

the capacitance and conductance value in the accumulation region.

At the higher gamma doses the value of capacitance and conductance of the Al/ TeO2/n-Si (MOS) structures are decreases due to radiation induced damage in the oxide. At higher doses the cluster formation is occurred inside the TeO2 film and produced easy conduction path to transport the current

It has been observed that for Al/TeO2/n-Si (MOS) structures having thickness 200

nm the catastrophic breakdown voltage to the measured capacitance and measured conductance plots as a function of gate voltage. It has also observed that the catastrophic breakdown voltage reduced irradiate MOS structure

Generally, TeO2 is polarized material at certain voltage polarization takes

maximum value that is very much depends on thickness of thin films of TeO2. In

the C-V and G-V plot of Al/TeO2/n-Si (MOS) structures having thickness of

tellurium dioxide (TeO2) layer 200 nm which is comparable thicker it has been

observed the shooting point at certain voltage at which polarization takes maximum value.

When radiation exposed to the films this catastrophic breakdown voltage reduced due to radiation-induced decease of εr

From the measured Cm-V and Gm-V plots for Al/ TeO2/n-Si MOS structures

having 100, 150 and 200 nm the series resistances were calculated before and after

gamma irradiation by the using equation which is shown in figure 1(c) , 2(c) and 3(c)

respectively.

2),(,2,

accmCaccmG

accmGsR

During the process of film deposition, some intrinsic defects are always

formed. The interaction of gamma radiation induces defects during its

passage through the thin film resulting into disorder in the microstructure of

the film. At small doses, these thin films have fine homogeneous grain

structure without any big pores and the number of defects (induced plus

residual intrinsic) is smaller than the number of intrinsic defects due to the

recombination of defects. The recombination of defects reduces the

resistivity of the thin film, giving rise to decrease the series resistance.

plots

-6 -4 -2 0 2 4 6

0.10

0.15

0.20

0.25

0.30

0.35

As-deposited 30 Gy 35 Gy 50 Gy 70 Gy 100 Gy

Thickness = 100 nm

Measu

red

Cap

acit

an

ce (

nF

)

Bias Voltage(V)

The measured capacitance (Cm) as a function of the Bias voltage before

and after gamma irradiation at different dose levels for Al/TeO2/n-Si

MOS structure having thickness of TeO2 layer 100 nm

Figure (1a)

-8 -6 -4 -2 0 2 4 6 80.10

0.15

0.20

0.25

0.30

0.35

Measu

red

Cap

acit

an

ce (

nF

)

Bias voltage(V)

Thickness = 150 nm

As-deposited 35 Gy 70 Gy 120 Gy 150 Gy

The measured capacitance (Cm) as a function of the Bias voltage before

and after gamma irradiation at different dose levels for Al/TeO2/n-Si

MOS structure having thickness of TeO2 layer 150 nm

Figure (2a)

-6 -4 -2 0 2 4 6

0.12

0.18

0.24

0.30

0.36

Thickness=200 nm

Measu

red

cap

acit

an

ce (

nF

)

Bias Voltage(v)


The measured capacitance (Cm) as a function of the Bias voltage before and

after gamma irradiation at different dose levels for Al/TeO2/n-Si MOS

structure having thickness of TeO2 layer 200 nm

Figure (3a)

-8 -6 -4 -2 0 2 4 6 80.00

0.08

0.16

0.24

0.32

Thickness 100 nm

Bias Voltage(V)


Measu

red

Co

nd

ucta

nce (

nF

)

The measured conductance (Gm/ω) as a function of the Bias voltage

before and after gamma irradiation at different dose levels for Al/TeO2/n-

Si MOS structure having thickness of TeO2 layer 100 nm

Figure (1b)

-8 -6 -4 -2 0 2 4 6 80.00

0.08

0.16

0.24

0.32

0.40Thickness 150 nm


Measu

red

Co

nd

ucta

nce (

nF

)

Bias Voltage (V)

The measured conductance (Gm/ω) as a function of the Bias voltage

before and after gamma irradiation at different dose levels for Al/TeO2/n-Si MOS structure having thickness of TeO2 layer 150 nm

Figure (2b)

-6 -4 -2 0 2 4 6

0.011

0.022

0.033

0.044

0.055

Thickness 200 nm


Measu

red

Co

nd

ucta

nce (

nF

)

Bias Voltage (V)

The measured conductance (Gm/ω) as a function of the Bias voltage before

and after gamma irradiation at different dose levels for Al/TeO2/n-Si MOS

structure having thickness of TeO2 layer 200 nm

Figure (3b)

-6 -4 -2 0 2 4 6200

300

400

500

600


Thickness = 100 nm

RS

Bias Voltage (V)

The Bias voltage dependence of the series resistance (Rs) at 1MHz at

room temperature before and after gamma irradiation at different dose levels for Al/TeO2/n-Si MOS structure having thickness of TeO2

layer 100 nm

Figure (1c)

-8 -6 -4 -2 0 2 4 6 8

250

300

350

400

450

500

Rs

Thickness = 150 nm


Bias Voltage(V)


room temperature before and after gamma irradiation at different dose levels for Al/TeO2/n-Si MOS structure having thickness of TeO2 layer

150 nm

Figure (2c)


room temperature before and after gamma irradiation at different dose levels for Al/TeO2/n-Si MOS structure having thickness of TeO2

layer 200 nm

-6 -4 -2 0 2 4 645

60

75

90


Thickness = 200 nm

Rs

Bias Voltage(V)

Figure (3c)

Future works is to be done the radiation induced change the real

permitivity, imaginary permitivity and density of interface state (Dit) form

corrected capacitance and conductance plot of Al/TeO2/n-Si MOS structure of

several thickness.

Future work

60Co -ray irradiation effects on the interface traps density of tin oxide films of

different thicknesses on n-type Si (111) substrates; N. Tuğluoğlu;Nuclear

Instruments and Methods in Physics Research B 254 (2007) 118–124

Analysis of electrical of Au/SiO2/n-Si(MOS)capacitors using the high-low

frequency capacitance and conductance methods; A.Tataroğlu Ş.altindal;

Microelectronic Engineering 85(2008)2256-2260

Effects of gamma irradiation on dielectric characteristics of SnO2 thin films; B.

Selcuk, S. B. Ocak and F. Yuksel; Nuclear Instruments and Methods in Physics

Research A 594 (2008) 395 – 399

References

Effect of ionizing radiation on MOS capacitors; R.K.chauhan, P.chakrabarti ;Microelectronic journal ;33 (2002) 197-203

Influence of Gamma radiation on Thin Ta2o5 –Si Structure ; E.Atanassova,

A. Paskaleva, R. Konakov, D.Spassov, M.V. Mitin ; Microelectronic journal 32 (2001) 553-562

Radiation-induced color centers. in La- doped PbWO crystals; Q.Deng, Z.Yin and R. Zhu; Nuclear Instrumentation and Methods A 438 (1999) 415–420

E. H. Nicollian and J. R. Brews, 1. MOS Physics and Technology (New York: Wiley, 1982), 224

Thank you

gamma radiation induced on teo2 thin film of dielectric properties

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