Characterization of charge trapping processes in fully-depleted UNIBOND SOI MOSFET subjected to γ-irradiation
An investigation of radiation effect on edgeless accumulation mode (AM) p-channel and fully-depleted enhancement mode (EM) n-channel MOSFETs, fabricated on UNIBOND silicon on insulatior wafers (SOI), is presented in the paper. Characterization of trapped charge in the gate and buried oxides of the...
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
2006
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| Цитувати: | Characterization of charge trapping processes in fully-depleted UNIBOND SOI MOSFET subjected to γ-irradiation / Y. Houk, A.N. Nazarov, V.I. Turchanikov, V.S. Lysenko, S. Andriaensen, D. Flandre // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2006. — Т. 9, № 2. — С. 69-74. — Бібліогр.: 7 назв. — англ. |
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irk-123456789-1214362017-06-15T03:04:46Z Characterization of charge trapping processes in fully-depleted UNIBOND SOI MOSFET subjected to γ-irradiation Houk, Y. Nazarov, A.N. Turchanikov, V.I. Lysenko, V.S. Andriaensen, S. Flandre, D. An investigation of radiation effect on edgeless accumulation mode (AM) p-channel and fully-depleted enhancement mode (EM) n-channel MOSFETs, fabricated on UNIBOND silicon on insulatior wafers (SOI), is presented in the paper. Characterization of trapped charge in the gate and buried oxides of the devices was performed by measuring only the front-gate transistors. It was revealed that the irradiation effect on EM n-MOSFET is stronger than that on AM p-MOSFET. Radiation-induced positive charge in the buried oxide proved to invert back interface what causes back channel creation in EM n-MOSFET but no such effect in AM p-MOSFET has been not observed. The effect of improving the quality of both interfaces for small irradiation doses is demonstrated. 2006 Article Characterization of charge trapping processes in fully-depleted UNIBOND SOI MOSFET subjected to γ-irradiation / Y. Houk, A.N. Nazarov, V.I. Turchanikov, V.S. Lysenko, S. Andriaensen, D. Flandre // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2006. — Т. 9, № 2. — С. 69-74. — Бібліогр.: 7 назв. — англ. 1560-8034 PACS 85.30.Tv, 85.30.De, 81.40.Wx http://dspace.nbuv.gov.ua/handle/123456789/121436 en Semiconductor Physics Quantum Electronics & Optoelectronics Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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English |
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An investigation of radiation effect on edgeless accumulation mode (AM) p-channel and fully-depleted enhancement mode (EM) n-channel MOSFETs, fabricated on UNIBOND silicon on insulatior wafers (SOI), is presented in the paper. Characterization of trapped charge in the gate and buried oxides of the devices was performed by measuring only the front-gate transistors. It was revealed that the irradiation effect on EM n-MOSFET is stronger than that on AM p-MOSFET. Radiation-induced positive charge in the buried oxide proved to invert back interface what causes back channel creation in EM n-MOSFET but no such effect in AM p-MOSFET has been not observed. The effect of improving the quality of both interfaces for small irradiation doses is demonstrated. |
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Article |
| author |
Houk, Y. Nazarov, A.N. Turchanikov, V.I. Lysenko, V.S. Andriaensen, S. Flandre, D. |
| spellingShingle |
Houk, Y. Nazarov, A.N. Turchanikov, V.I. Lysenko, V.S. Andriaensen, S. Flandre, D. Characterization of charge trapping processes in fully-depleted UNIBOND SOI MOSFET subjected to γ-irradiation Semiconductor Physics Quantum Electronics & Optoelectronics |
| author_facet |
Houk, Y. Nazarov, A.N. Turchanikov, V.I. Lysenko, V.S. Andriaensen, S. Flandre, D. |
| author_sort |
Houk, Y. |
| title |
Characterization of charge trapping processes in fully-depleted UNIBOND SOI MOSFET subjected to γ-irradiation |
| title_short |
Characterization of charge trapping processes in fully-depleted UNIBOND SOI MOSFET subjected to γ-irradiation |
| title_full |
Characterization of charge trapping processes in fully-depleted UNIBOND SOI MOSFET subjected to γ-irradiation |
| title_fullStr |
Characterization of charge trapping processes in fully-depleted UNIBOND SOI MOSFET subjected to γ-irradiation |
| title_full_unstemmed |
Characterization of charge trapping processes in fully-depleted UNIBOND SOI MOSFET subjected to γ-irradiation |
| title_sort |
characterization of charge trapping processes in fully-depleted unibond soi mosfet subjected to γ-irradiation |
| publisher |
Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
| publishDate |
2006 |
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http://dspace.nbuv.gov.ua/handle/123456789/121436 |
| citation_txt |
Characterization of charge trapping processes in fully-depleted UNIBOND SOI MOSFET subjected to γ-irradiation / Y. Houk, A.N. Nazarov, V.I. Turchanikov, V.S. Lysenko, S. Andriaensen, D. Flandre // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2006. — Т. 9, № 2. — С. 69-74. — Бібліогр.: 7 назв. — англ. |
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Semiconductor Physics Quantum Electronics & Optoelectronics |
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2025-07-08T19:53:46Z |
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2025-07-08T19:53:46Z |
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| fulltext |
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2006. V. 9, N 2. P. 69-74.
© 2006, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
69
PACS 85.30.Tv, 85.30.De, 81.40.Wx
Characterization of charge trapping processes
in fully-depleted UNIBOND SOI MOSFET subjected to γ-irradiation
Y. Houk,1 A.N. Nazarov,1 V.I. Turchanikov,1 V.S. Lysenko,1
S. Andriaensen,2 and D. Flandre 2
1V. Lashkaryov Institute of Semiconductor Physics, NAS of Ukraine,
45, prospect Nauky, 03028 Kyiv, Ukraine,
2DICE, Universite Catholique de Louvain, Louvain-la-Neuve, Belgium
Abstract. An investigation of radiation effect on edgeless accumulation mode (AM)
p-channel and fully-depleted enhancement mode (EM) n-channel MOSFETs, fabricated
on UNIBOND silicon on insulatior wafers (SOI), is presented in the paper.
Characterization of trapped charge in the gate and buried oxides of the devices was
performed by measuring only the front-gate transistors. It was revealed that the
irradiation effect on EM n-MOSFET is stronger than that on AM p-MOSFET. Radiation-
induced positive charge in the buried oxide proved to invert back interface what causes
back channel creation in EM n-MOSFET but no such effect in AM p-MOSFET has been
not observed. The effect of improving the quality of both interfaces for small irradiation
doses is demonstrated.
Keywords: SOI, MOSFET, radiation, small-dose improvement.
Manuscript received 06.10.05; accepted for publication 29.03.06.
1. Introduction
Thin-film SOI EM and AM MOSFETs are very
attractive as basic elements of CMOS integrated circuits
for high-temperature applications [1]. But due to the
charge coupling effect [2] and the presence of thick
buried oxide (BOX) in SOI wafers these elements have
to be less radiation-resistant to a total dose. The purpose
of the present work is to study the radiation effect on
SOI MOSFETs that are devoted to high-temperature
applications – such investigation has not yet been
performed. Besides, we use the double derivation
method [3-5] applied only to front-gate characteristics of
SOI MOSFETs to extract the charges generated both in
the gate and buried oxides during irradiation, in contrast
to usual extraction of radiation charge generated in the
BOX, which needs carrying out back-gate SOI
MOSFETs measurements [6, 7].
2. Experimental
Fully-depleted (FD) EM n- and AM p-MOSFETs
(Fig. 1a) fabricated in the same chip using UNIBOND
SOI material have been investigated. After device
processing the BOX, silicon film and gate oxide
thicknesses were 360, 80 and 38 nm, respectively. The
doping channel concentration was 5⋅10
16
cm−3. Edgeless
devices with L/W = 3/172 μm were considered in order
to avoid edge effects. For irradiation, the 60Co gamma-
ray source with the flux of 390 rad/s has been used. The
MOSFETs were shorted during irradiation.
Transfer characteristics (drain current vs gate voltage
DI
1GV ) as a function of the bias applied to the silicon
substrate
2GV (see Fig. 1b) were measured at room
temperature in the linear regime ( V1.0=DV ). First and
second derivatives of DI
1GV characteristics were
calculated numerically.
3. Theory
The most clearly the effect of the radiation on the SOI
MOSFETs is revealed in the change of transfer
characteristics of the devices: as seen from Fig. 2, the
transfer characteristics are shifted to the left, both for FD
EM (Fig. 2a) and AM MOSFETs (Fig. 2b). In other
words, the threshold voltage of the characteristics
decreases with increasing the radiation dose regardless
of the type of the irradiated transistor. As will be shown
below, careful investigation of transfer characteristics,
measured only on the front-gate, allows to determine all
possible parameters of radiation-induced charge trapping
in the gate and BOX of the transistors.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2006. V. 9, N 2. P. 69-74.
© 2006, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
70
Si
Si p-type
SiO2
p
+ p
+
Si
Si p-type
SiO2
Back gate
Front gate
Substrate
Front gate
Oxide (SiO )2
Buried
Oxide
Film
360 nm
80 nm
38 nm
p
+ p
+
(b)(a)
Fig. 1. SOI AM p-MOSFET cross-section (a); measurement scheme used (b).
Fig. 2. Illustration of the radiation effect on MOSFETs: transfer characteristics of SOI FD EM n-MOSFET (a) and those of SOI
AM p-MOSFET (b) at various radiation doses.
In Figs 3a and 3a', showed are the transfer
characteristics DI
1GV for high-dose irradiated FD EM
n-MOSFETs and AM p-MOSFETs at room temperature.
Correspondingly below them, the plots of their first
derivatives, or transconductances, are depicted (Figs 3b
and 3b'). The front-gate transconductance curves allow
to calculate the mobilities of the charge carriers both in
the front and back interfaces of the transistor. The
mobility of the charge carriers in the front channel, μ1, of
the MOSFETs is calculated from the maximum
transconductance under the depletion condition at the
BOX/silicon film interface, maxg (see Fig. 3b) [1]:
SVW
gLC maxox
1
1=μ , (1)
where L and W are, respectively, the length and the
width of the channel,
1oxC is the capacitance of the gate
oxide, and SV is the source voltage. The mobility in the
back channel 2μ is calculated from the plateau observed
in the front-channel transconductance plateaug (see
Fig. 3b) by the following formula [1]:
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
++=
1
1
1 oxox
Si
max
plateau
12 1
C
C
C
C
g
g itμμ , (2)
neglecting the capacitance of the front surface states,
1itC (see Appendix), to obtain a minimal estimation of
the back channel mobility. SiC is the capacitance of the
Si film.
Transconductance derivatives, or 2nd derivatives of
transfer characteristics, with respect to
2GV are shown
in Figs 3c and 3c'. The front-gate threshold voltages of
the MOSFETs for front and back channels are easily
determined as the positions of the peaks of these
characteristics (see Fig. 4) [3].
A typical dependence of AM p-MOSFET front-gate
channel voltages for front and back channels on con-
ditions at the back interface is illustrated in Fig. 5a [5].
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2006. V. 9, N 2. P. 69-74.
© 2006, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
71
Fig. 3. DI GV characteristics for edgeless EM n-MOSFET (a) and AM p-MOSFET (a'), irradiated with the total dose of
1·106 rad, EM (b) and AM (b') MOSFETs transconductance, and derivatives of transconductance for EM (c) and (AM) (c')
MOSFETs.
From available dependences, it is possible to derive
radiation-induced dynamical change of the fixed charge
on the gate oxide and BOX as well as surface state
capacitances for both front and back interfaces. The
respective calculations can be performed most simply
for the AM p-MOSFET, for which DI
1GV
characteristics are weakly affected by a back channel
current, and the front channel threshold voltage can be
derived easily.
Indeed, in the case of the inverted back interface
( F2
2
φψ =s ) we observe the saturated
1thV vs
2GV
dependence for high positive
2GV values, and it is
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2006. V. 9, N 2. P. 69-74.
© 2006, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
72
Fig. 4. The illustration of the 2nd derivative method of
threshold voltage determination.
Fig. 5. Front-gate threshold voltages for front and back
channels of AM p-MOSFET depending on conditions at the
back interface (a) and an illustration of the radiation-induced
charge parameters extraction from the dependences of the
threshold voltages upon back-gate voltages (b).
possible to obtain the radiation-induced charge
1fQΔ in
the gate oxide, knowing the front-channel voltage shift
1thVΔ for the interface of this type (see Fig. 5b) [5]:
111
1
1
ox
Si
ox
Si
F
ox
th 2
2
C
Q
C
C
C
Q
V f −−−= φ . (3)
In the case of a depleted back interface, we have a
linear decrease in the front-channel threshold voltage
1thV vs back-gate voltage
2GV , which is described by
the following expression [5]:
]).
2
[(
)(2
22
2
22
221
2
11
1
1
ox
Si
ox
Sioxox
oxSi
ox
Si
ox
th
C
Q
C
Q
V
CCCC
CC
C
Q
C
Q
V
f
msG
it
f
−−−×
×
++
−−−=
φ
(4)
From the slope of this linear dependence, we can
obtain the capacitance of the back-interface states
2itC .
Now, knowing
1fQΔ and
2itC we can find the radiation-
induced charge
2fQΔ in the BOX from the horizontal
shifts
2GVΔ of the
1thV vs
2GV curves in the same region
(see Fig. 5b). Finally, from the slope of the linear
dependence of the front-gate threshold voltage for the
back channel with the condition of weak accumulation
at the back interface (see Fig. 5b), we can obtain the
capacitance of the front-interface states
1itC [5]:
]).
2
[(
1
2
22
2
22
2
1
1
11
1
2
ox
Si
ox
Si
ox
ox
Si
ox
Si
ox
th
C
Q
C
Q
V
C
C
C
CC
C
Q
C
Q
V
f
msG
itf
−−−×
×⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛ +
+−−−=
φ
(5)
4. Results and discussion
The threshold voltage shift in the front and back
transistors at zero back-gate voltage as a function of
irradiation dose is presented in Fig. 6 that demonstrates a
stronger irradiation effect on the threshold of the front
channel for the AM p-MOSFET than for the EM n-
MOSFET. Such a phenomenon is possibly associated
with a compensative effect of the radiation induced
positive oxide charge in the gate oxide and negatively
charged surface states on the threshold voltage of the
EM n-MOSFET and the overall effect of the positive
oxide charge and positively charged surface states on the
threshold voltage of the AM p-MOSFET.
Additionally, an apparent threshold voltage shift in
the MOSFETs, which is defined as the front-gate voltage
from which the drain current starts to significantly
increase in the linear regime [5], is also presented in
Fig. 6. It should be noted that, in the case of the apparent
threshold voltage shift with irradiation, the AM p-
MOSFET appears to be more radiation-resistant than
EM n-MOSFET. This is associated with inversion
channel creation at the back interface of the EM n-
MOSFET with positive charge generation in the BOX
during gamma-irradiation. Thus, for the EM n-MOSFET
we can observe a good correlation of the shift of the
apparent threshold voltage with the physical threshold
voltage shift for the back channel (see Fig. 6). That is
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2006. V. 9, N 2. P. 69-74.
© 2006, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
73
Fig. 6. Threshold voltage shifts for EM n- and AM p-
MOSFETs. The apparent threshold voltage is defined as the
front-gate voltage from which the drain current starts to
significantly increase in the linear regime [5].
Fig. 7. The front and back channel mobilities for EM n- and
AM p-MOSFETs.
Fig. 8. The front channel threshold voltage of AM p-
MOSFET vs back-gate voltage for various irradiation doses
(a) and radiation induced charges in the gate and buried
oxides of AM p-MOSFET as well as surface state density at
the BOX/Si film interface (b). Radiation induced BOX charge
in MOSFET made by similar UNIBOND technology is
plotted by Gruber et al. [7].
why it is impossible to use the apparent threshold
voltage to determine charges both in gate and buried
oxides for EM n-MOSFETs.
Fig. 7 depicts the change of electron and hole mobility
in the front and back channels of the MOSFETs. It should
be noted that on the small dose irradiation (within the
range 103 to 104 rad) an increase of the electron and hole
mobilities is observed. This effect can be related with
radiation ordering of the gate oxide/silicon film interface
as well as the BOX/silicon film interface.
As shown in the previous section, the radiation
induced charge in the gate oxide, buried oxide and
interfaces can be calculated from the front channel
threshold voltage
1thV vs back-gate voltage
2GV
characteristics as a function of the irradiation dose (see
Fig. 8a). The results of the calculations for AM p-
MOSFET are presented in Fig. 8b. The important point
is in the fact that the radiation induced positive charge in
the BOX in our MOSFETs is smaller than that presented
in Ref. [7] (see Fig. 8b) for similar UNIBOND
technology. Fortunately, in recent years considerable
efforts for developing the UNIBOND technique have
improved the quality of the BOX in such SOI structures.
Additionally it is noteworthy that the interface surface
state density in the BOX/Si film interface reveals a
minimal value in the dose range from 103 to 104 rad.
This phenomenon indicates an increase of electrical
quality of the back interface as well as the gate oxide/Si
film interface after small dose irradiation.
5. Conclusions
The radiation effect on edgeless FD EM n-MOSFETs
and AM p-MOSFETs was investigated in the present
paper. The used 2nd derivative method of threshold
voltage extraction allowed to distinguish unambiguously
the front-gate threshold voltages for the front and back
channels and to determine the concentration of the radia-
tion induced charges in the SOI MOSFETs by carrying
out only the front-gate measurements. Following small
doses of irradiation, an increase of the charge carrier
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2006. V. 9, N 2. P. 69-74.
© 2006, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
74
mobility both in front and back channels and decrease of
the surface state density in the BOX/Si film interface are
observed, what takes place due to an increase of the qua-
lity of the structural and electrical properties of the gate
oxide/film interface as well as the BOX/film interface.
Appendix
Indices 1 and 2 denote quantities corresponding to front
(1) and back (2) interface.
q electron charge
aN channel doping
L , W , Sit length, width and thickness of Si-
film
2,1msφ metal-semiconductor work
functions
2,1sψ surface potentials
2,1fQ oxide fixed charges
2,1cQ surface channel charges
SiSi tqNQ a−= depletion charge
2,12,1 itit qDC = interface-trap capacitances
2,1itD average concentrations of
interface traps
2,1oxC oxides capacitances
SiC Si film capacitance
2,1GV gate voltages
DSV , source and drain voltages
2,1thV threshold voltages
DI drain current
g transconductance
2,1μ mobilities
Acknowledgements
The authors thank the technical staff of the UCL
Microelectronics Lab for device fabrication. This work
has been supported by STCU project No 2332.
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