Semiconductor Based Hydrogen Sensor and
Detecting System
Reporter: Dr. Kun-Wei Lin
1
Outline
Part 1
Introduction
Part 2
Experimental
Part 3
Gas Sensing Characteristics of the Different Structure –
Based Sensors
Part4 96、98、99 Projects
some application
2
Part 1
Introduction
3
4
摘錄自網路
5
Applications of Hydrogen
Hydrogen
Fuel Cell
Hydrogen Cylinder
Hydrogen
Transportation
Hydrogen
Storage
Hydrogen
Applications
Helios Prototype
Hydrogen
Liquid hydrogen fueled aircraft
Refueling Station
Hydrogen
-Domestic Use
6http://www.mae.ufl.edu/NasaHydrogenResearch/index.php?src=h2webcourse
Hydrogen
fueled aircraft
Introduction
Ingemar Lundström
Since 1976, Transistors and Schottky diodes
based on Metal(Pd)-Oxide-Semiconductor(Si)
MOS devices were used as hydrogen sensors.
—Lundstrom’s Group (Linkoping University, Sweden)
Application of hydrogen sensor
＊ Industrial fabrication processes
＊ Medical installations
＊ Laboratories (especially for semiconductor fabrication)
＊ Hydrogen-fueled motor vehicles
7
Types of Hydrogen Sensors
Schottky diode
Metal
Field-effect
transistor
Capacitor
Metal
Insulator
S
Metal
Insulator
D
Semiconductor
Semiconductor
Semiconductor
Different type of gas sensors
＊ MOS capacitors (capacitance change)
＊ MOS field effect transistors (threshold voltage shift)
＊ MOS Schottky
barrier diodes (current change)
Gain=
＊ MS Schottky barrier diodes (current change)
8
8
The advantages of our device
compare with Si-based structure
＊ Short response time
＊ Obvious current variation
＊ Operation at room temperature
＊ widespread operating temperature
regime
9
Mechanism of Hydrogen-Sensing
H2O (g)
H2(g)
O2(g)
ΔHS
OHa Ha
Oa Oa
Pd or Pt
catalytic metal
Ha
Ha
Surface
Hb
-
-
-
+
+
+
ΔHb
ΔHi
Oxide
ΔHio
Semiconductor
H2(g) : molecular hydrogen
Ha : adsorbed hydrogen atoms on the Pd or Pt surface
Hb : hydrogen atoms in the Pd or Pt bulk
H i: hydrogen atoms at the Pd/oxide interface
10
Pd
Interface
Mechanism of Hydrogen-Sensing
Under atmospheric conditions
The catalytic reaction kinetics scheme of hydrogen adsorption
and desorption
H2(g)
k1
k2
2Ha
r1
k3
2Hb
r2
2Hi
r3
where k1, k2, k3, and r1, r2 and r3 are adsorption and desorption rate constants.
 In presence of oxygen, the addition reaction of hydrogen
desorption
11
O2 + 2Ha
2(OHa)
OHa + Ha
H2O
Mechanism of Hydrogen-Sensing
Under steady-state conditions, b induced by hydrogen adsorption
can be assumed as
b  b max i
where b,max is the maximum change in barrier height and i is
the hydrogen coverage at the interface.
i
K
1  i
PH 2
PO2

where K is a temperature-dependent rate constant; PH2 and
PO2 are H2 and O2 partial pressures, respectively. The
reaction order  1 for temperatures above 75℃ and  0.5
for the lower temperatures
12
12
Mechanism of Hydrogen-Sensing
The Langmuir form can be expressed in terms of B and Bmax as

Po2
1
1
1



 K  PH  max  max
2
From the relation of saturation current and barrier height, the
Langmuir can also be deduced as
Po2
1
1
1



I0g
I 0 g ,max
I 0 g ,max
PH2
ln( ) K ln(
)
ln(
)
I0
I0
I0
where I0g,max is the maximum saturation current at hydrogencontained ambient.
13
Mechanism of Hydrogen-Sensing
According to the van’t Hoff equation
 H S
ln K 

RT
R
where H is the change of enthalpy, S the change of entropy,
and R the gas constant.
The change of barrier height b can be rewritten as:
b, max 
14
1  KPH1 /2 2
1/ 2
H2
KP
 b
The schematic setup of the
hydrogen measurement system
Stainless Steel
Chamber
Heating
Tape
Mass Flow
Control
Sample
Valve
Valve
Manometer
Exhaust
Test Line
Heater
Flange
Semiconductor Parameter Analyzer
Air
15
H2/Air Mixture
Heater and Thermometer
Measurement system implementation
Agilent 4155C
半導體量測平台
感測氣瓶
16
16
Measurement system
implementation
17
17
Part 2
Experimental
18
Fabrication of the Device
Pd Schottky
Contact
AuGe Ohmic
Contact
300Å n+-GaAs
50Å Thermal Oxide
3000Å AlGaAs active layer(n=2x1017cm-3 )
5000Å GaAs buffer layer
S.I. GaAs substrate
 Thin films were grown by
MOCVD on S.I. GaAs
substrate.
 Conventional
photolithography and wet
etching technique is used.
 Thermal oxide was grown
by furnace at 120oC for 60
minutes.
 Metal pattern was made by
the thermal evaporation
method.
 The dimension of device is
2.05x10-3 cm2.
Pd Schottky
Contact
19
Ohmic
Contact
 Ohmic contact : AuGe
 Schottky contact : Pd
Why We Choose AlGaAs and Pd?





20
AlxGa1-xAs is lattice matched to GaAs, and the
mole fraction of Al can be changed from 0 to 1.
The energy bandgap of AlGaAs is larger than
GaAs and InP.
In compared with InGaP/GaAs and InP-based
material system, the thermal oxide is more
easily grown on AlGaAs/GaAs.
AlGaAs-based hydrogen sensor is suitable for
higher operation temperature than InP-based
system.
Pd metal shows excellent selectivity to
hydrogen gas than other metals.
Hydrogen Sensing Mechanism

Air
Pd Metal
Oxide
AlGaAs

- +on Pd
H2 adsorb
Dipole
surface
- +and
Layer
H atoms
dissociate
- + into
H2
atomsdiffuse into
Pd bulk
molecule


Ec
FermiLevel
Ev
21

Steps of H2 sensing
mechanism :
H2 molecules adsorb
on Pd surface and
then dissociate to
atoms.
H atoms diffuse into
the bulk of Pd metal.
H atoms adsorb on
Pd/oxide interface
and form thin dipole
layer.
The barrier height is
reduced by the
formation of thin
dipole layer.
Current-Voltage Characteristics
o
Pd/oxide/AlGaAs at 30 C
o
Pd/oxide/AlGaAs MOS Schottky Diode at 95 C
1E-3
0.01
1E-4
Air
15ppm (H2/Air)
50ppm
100ppm
200ppm
500ppm
0.1%
0.5%
1%
1E-4
Current (A)
1E-5
1E-6
1E-5
Air
15ppm
50ppm
100ppm
200ppm
500ppm
0.1%
0.5%
1%
1E-6
Current (A)
1E-3
Forward Bias
1E-7
1E-8
1E-9
1E-10
1E-11
1E-12
1E-7
1E-13
0.0
1E-8
0.2
0.4
0.6
0.8
1.0
Applied Voltage (V)
1E-9
Reverse bias
1E-10
1E-11
0.0
0.2
0.4
0.6
Applied Voltage (V)
0.8
1.0
 The Pd/oxide/AlGaAs
MOS device shows
excellent performance
from room temperature
to 160oC
22
Barrier Height at Room Temperature
Barrier Height Compared with InGaP
1.05
InGaP
AlGaAs
Barrier Height (eV)
1.00
0.95
 0.92eV in air
 0.77eV in 1% H2/air
0.90
 AlGaAs
 1.05eV in air
 0.84eV in 1% H2/air
0.85
0.80
0.75
0
2000
4000
6000
8000
Hydrogen Concentration (ppm)
23
 In compared with
InGaP-based device,
the barrier height of
AlGaAs-based device is
larger.
 InGaP
10000
Barrier Height Variation
•
Barrier Height Variation
0.22
Barrier Height Variation (eV)
0.20
•
InGaP
AlGaAs
0.18
0.16
0.14
•
0.12
0.10
Barrier height variation at
room temperature.
The barrier height variation of
the AlGaAs-based device is
larger than the InGaP-based
device from 15ppm to 1% of
hydrogen gas concentration.
Barrier height variation of
InGaP & AlGaAs are 0.14 and
0.21 eV, respectively.
0.08
0.06
0.04
100
1000
10000
Hydrogen Concentration (ppm)
24
Saturation Sensitivity
Saturated Sensitivity at 0.35V Forward Bias
180
160
30 C
o
50 C
o
70 C
o
95 C
o
120 C
o
160 C
140
120
Sensitivity (S)
S=
o
100
60
40
20
0
2000
4000
6000
8000
Hydrogen Concentration (ppm)
25
2
Iair
80
0
IH - Iair
10000
 Pd/oxide/AlGaAs MOS
device shows very high
saturation sensitivity,
especially at room
temperature.
 Over 155 times of
sensitivity can be
observed in 1% H2/Air
at room temperature.
Saturation Sensitivity at R.T.
Saturated Sensitivity at Several Apply Voltage
180
0.3V
0.4V
0.5V
0.6V
0.7V
0.8V
160
140
Sensitivity (S)
120
100
80
60
40
20
0
-20
0
2000
4000
6000
8000
Hydrogen Concentration (ppm)
26
10000
 The saturation
sensitivity is decreased
with increasing the
applied voltage.
 Generally, the
saturated sensitivity is
increased with
increasing the
hydrogen
concentration.
 The saturated
sensitivity is almost
unity when the applied
voltage is over 0.8V.
Transient Response at 30oC
o
Transient Response of Pd/Oxide/AlGaAs at 30 C
-8
2.4x10
-8
2.2x10
-8
2.0x10
-8
1.8x10
-8
1.6x10
-8
1.4x10
-8
1.2x10
-8
1.0x10
-9
8.0x10
-7
8.0x10
-7
7.0x10
-7
Current (A)
6.0x10
-7
5.0x10
-7
4.0x10
0
1000
2000
4000
Conc.of H2/Air
15ppm
50ppm
100ppm
200ppm
500ppm
0.1%
0.5%
1%
-7
3.0x10
-7
2.0x10
-7
1.0x10
0.0
0
1000
2000
3000
4000
5000
Time(sec)
27
3000
6000
7000
8000
 The applied voltage is
0.35V.
 Even at room
temperature, the
studied device shows
good transient response
characteristics under
extremely low hydrogen
concentration of 15 ppm
H2/Air.
 The maximum current of
the studied device
varies from 1.5x10-8 to
7.7x10-7 A under the
condition of Air and
H2/Air, respectively.
Transient Response at 95oC &
160oC
o
o
Transient Response of Pd/Oxide/AlGaAs at 160 C
Transient Response of Pd/Oxide/AlGaAs at 95 C
4.5x10
-4
4.0x10
-4
3.5x10
-4
3.0x10
-4
2.5x10
-4
2.0x10
-4
-5
-6
1.5x10
-4
1.0x10
4000
-4
-5
4.0x10
-5
3.5x10
15ppm
50ppm
100ppm
200ppm
500ppm
1000ppm
5000ppm
10000ppm
-5
3.0x10
-5
Current(A)
2.5x10
-5
2.0x10
-5
1.5x10
1.0x10
5.0x10
0
1000
2000
Time(sec)
28
3000
15ppm
50ppm
100ppm
200ppm
1000ppm
5000ppm
10000ppm
0
1000
2000
Time(sec)
3000
4000
Response of 1% Hydrogen
τa
τb
30oC
66
50
50oC
26
18
70oC
11
10
95oC
10
8
120oC
8
6
160oC
2
1.5
Transient Response of 1% Hrdrogen Gas
1E-3
o
160 C
o
120 C
1E-4
o
95 C
o
Current (A)
70 C
1E-5
o
50 C
Air purge in
1E-6
o
30 C
1E-7
H2/Air purge in
1E-8
0
5000
10000
15000
Time (sec)
29
20000
25000
 τa : adsorption time
constant,
 τb : adsorption time constant
are defined as the times
reach e-1 of the final steadystate current values.
Conclusion
 At room temperature, the extremely hydrogen
concentration of 15ppm can be easily detected.
 The detected transient-state response characteristic
of 15ppm H2/air at room temperature is first
reported.
 The reverse current exhibit a highly sensitivity
linearity, the current change from 1x10-10A(air) to
1x10-8A(1%) at 95oC.
 High sensitivity of 155 under 0.3V and 1% H2/air can
be obtained at room temperature.
 The studied device shows a promise for high
sensitivity, low leakage current, wide temperature
operation regime and fast response speed for
hydrogen sensor application.
30
Comparative studies of hydrogen sensing
performance of Pd/InGaP MOS and MS
Schottky diodes
31
The X-ray energy dispersive spectrometer
(EDS能量散射) analysis
32
Measured I-V characteristics of the studied
Pd/InGaP MOS Schottky diode
Measured I-V
the studied
Schottky diode,
atmospheric
characteristics of
Pd/InGaP MOS
at T=400K, under
condition
with
different hydrogen concentrations.
The inset of this figure shows
the corresponding forward I-V
characteristics of studied device
at different temperature of 300,
400, 500, 550, and 600K,
respectively.
33
Measured I-V characteristics of the studied
Pd/InGaP MS Schottky diode (400K)
Measured I-V characteristics
of the studied Pd/InGaP MS
Schottky diode, at T=400K,
under atmospheric condition
with
different
hydrogen
concentrations.
The current variation of MOS
structure is lager than that of MS
Schottky diode. This is attributed
to the reduction of the leakage
current
resulting
from
the
improved interface properties
under the presence of interficial
oxide layer.
34
Barrier height as a function of hydrogen
concentration in air
35
1
ln
I0g
I0
as a function of
PH21/ 2
Po2
1
1
1



I0g
I 0 g ,max
I 0 g ,max
PH2
ln( ) K ln(
)
ln(
)
I0
I0
I0
From slopes and intercepts, the
equilibrium constant K values are
obtained as 3.01, 1.38, and 0.7 for
the Pd-MOS Schottky diode at 350,
400, and 450K, respectively.
The equilibrium constant K is
decreased as the temperature is
increased.
36
1
ln
I0g
I0
1 / 2
P
as a function of H 2
The corresponding K values of
the studied Pd-MS Schottky diode
are 2.36, 2.11, and 1.85 at 350,
400,
and
450K,
respectively.
The equilibrium constant K is
decreased as the temperature is
increased.
The interface coverage i is
decreased with elevating the
temperature at the same hydrogen
partial pressure.
The water production rate is
increased with increasing the
operating temperature.
37
lnK as a function of the reciprocal of temperature
According to the van’t Hoff equation
ln K 
 H
RT
S

R
where H is the initial heat of hydrogen
adsorption, S the change of entropy, and R
the gas constant.
From slopes of this plot, the
calculated H values for Pd/InGaP
MOS and MS Schottky diodes are 355
and 65.9 meV/atom, respectively.
38
1/ 2
P
 i/(1-i) as a function of
H2
The change of barrier height b
can be rewritten as:
max 
1  KPH1 /2 2
1/ 2
H2
KP
 b
The calculated max values are
163, 103, 88.6, and 82 meV for PdMOS Schottky diode at 300, 350,
400, and 450K, respectively.
39
Transient response curves
Transient response curves upon
the introduction and removal of 97,
537, and 9090ppm H2/air gases of
the
studied
Pd/InGaP
MOS
Schottky diode at 400K.
With increasing the hydrogen
concentration
from
97
to
9090ppm H2/air, the response
time constant of adsorption (a) for
the studied MOS Schottky diode
is decreased from 35 to 5.4 sec.
40
Transient response curves
Transient response curves upon
the introduction and removal of 97,
537, and 9090ppm H2/air gases of
the studied Pd/InGaP MS Schottky
diode at 400K.
With increasing the hydrogen
concentration from 97 to 9090ppm
H2/air, the response time constant of
adsorption (a) for the studied MS
Schottky diode is decreased from 64
to 7.8 sec.
41
Transient response curves
 The transient response curves
of the studied MOS Schottky diode
at 350 and 400 K vary gradually
increase.
This implies that the coverage
sites at the Pd metal and oxide
interface are not all occupied and
the water production rate is lower
than adsorption rate.
 At a higher temperature of 600K,
the interface coverage sites are all
occupied and the water production
rate is larger than the adsorption
rate.
42
Transient response curves
 At low temperature of 350K,
the unsaturated behaviors of
transient response are found.
 At 400 and 500K, due to the
absence of interface coverage
site in MS Schottky diode, the
adsorption and absorption on
the Pd surface are depend on
the temperature and the Pd
surface property.
43
Summary
The Pd/InGaP hydrogen sensors based on the MOS and MS Schottky
diodes have been fabricated and studied. The studied devices exhibit
significantly wide operating temperature regimes.
Even at 300K and low hydrogen concentration of 15ppm H2/air, the
remarkable hydrogen detection can be observed.
Under the presence of oxide layer in device structure, the hydrogen
detection sensitivity is improved.
From the van’t Hoff equation, heats of hydrogen adsorption are 355 and
65.9 meV/atom for studied MOS and MS-type devices, respectively.
These values confirm that hydrogen atoms populated at the interface
between Pd metal and oxide layer causes the improved hydrogen
detection characteristics of MOS type structure.
44
Comparative studies of hydrogen
sensing performance of Pd- and
Pt- InGaP MOS Schottky diodes
45
Current-voltage (I-V) characteristics of PdInGaP MOS Schottky diode hydrogen sensor
The forward currents of the studied
Pd-InGaP MOS Schottky diode are
substantially
increased
with
increasing
the
hydrogen
concentration and temperature.
The current variations of InGaP
Schottky diode based on Pd metal
are more sensitivite than those of Pt
metal
under
low
hydrogen
concentration (< 937 ppm H2/air)
and low operating temperature (T<
400 K) regimes.
46
Current-voltage (I-V) characteristics of PtInGaP MOS Schottky diode hydrogen sensor
The forward currents of the studied
Pt-InGaP MOS Schottky diode are
substantially
increased
with
increasing
the
hydrogen
concentration and temperature.
At high operating temperature,
the Pt/InGaP sensor has better
detecting properties. Particularly, at
600K, the current variations of
Pt/InGaP Schottky diode are
significantly higher than those of
Pd/InGaP Schottky diode.
47
Current variation as a function of hydrogen
concentration
Current variation as a function
of hydrogen concentration for PdInGaP Pd-InGaP MOS Schottky
diode hydrogen sensors at
different temperature.
Upon exposing to low hydrogen
concentration ambient, however,
the Pd-InGaP Schottky exhibits
better
hydrogen
detecting
capability.
48
Current variation as a function of hydrogen
concentration
Current variation
function
of
concentration for
MOS Schottky diode
sensors
at
temperature.
as a
hydrogen
Pt-InGaP
hydrogen
different
By
comparing
with
the
hydrogen sensing response
from current variations, generally,
the Pt/InGaP Schottky diode is
more sensitive to hydrogen than
the Pd-InGaP Schottky diode.
49
Barrier height as a function of
hydrogen concentration
 Barrier height as a function
of hydrogen concentration for
Pd-InGaP MOS Schottky
diode hydrogen sensor at
different temperature.
The barrier height variation
is significant under low
hydrogen concentration for
Pd-InGaP
MOS
Schottky
diode.
50
Barrier height as a function of
hydrogen concentration
Barrier height as a function of
hydrogen concentration for PdInGaP MOS Schottky diode
hydrogen sensor at different
temperature.
Under the hydrogen-contained
ambient, the Pt-InGaP Schottky
diode exhibits a relatively large
reduction
of
b
magnitude
especially in high hydrogen
concentration regimes.
51
lnK as a function of the reciprocal of
temperature
Under this operating temperature
region, the hydrogen adsorption
processes of both studied devices
are exothermic. Hence, as the
temperature is increased, the
hydrogen
responses
are
unfavorable. Above 450K, on the
contrary, the slope of the studied
Pd/InGaP
Schottky
diode
is
negative. It is known that the
contact belongs to Schottky type if
the interface reaction heat is
positive. Yet, an Ohmic contact is
found
for
negative
interface
reaction heat.
52
Theoretical Modeling
Fogelberg and Petersson proposed a model:
Under atmospheric conditions, the hydrogen adsorbed
on Pd surface reacting with oxygen to form water can
be expressed as:
c1
H 2 
2H a
c2
O2  2 H a 
2[OH ]a
c3
OH a  H a 
H 2O
Based on the rate equations of hydrogen-oxygen reaction under
steady-state conditions, These rate equations describing the Pd
surface with oxygen present are :
d S 2 FH 2 S0 H 2
N d

(1  4 O  4 OH   S )  2c1 S2  c2 S O  c3 S OH  i i
dt
NS
N s dt
2 FO2 S 0O2
d O

(1  4 O  4 OH   S ) 2  c2 S O
dt
NS
d OH
 c2 S O  c3 S OH
dt
53
Theoretical Modeling
Ni
Number of sites per area at the interface
N*
Number of sites per area at the Pd surface
S0H2 Sticking coefficient for hydrogen
S0O2 Sticking coefficient for oxygen
HS
Heat of adsorption for hydrogen at the Pd surface
Hb
Heat of adsorption for hydrogen in the Pd bulk
Hi0
Initial heat of adsorption for hydrogen at the Pd/oxide interface
The molecular flux towards the surface and given by
F
P
2mkT
where k is the Boltzman constant and T the temperature. P denotes the
partial pressure of molecular hydrogen or molecular oxygen and m the
mass of molecular hydrogen or molecular oxygen.
54
Theoretical Modeling
The rate equation for hydrogen at the interface can be expressed as
d i
N*
N*

c4 S (1   i ) 
c5 i (1   S )
dt
Ni
Ni
where N* is the concentration of sites in the transition state, i the coverage of
hydrogen at the interface.
Under steady-state condition
d S d O d OH


0
dt
dt
dt
By substituting O and OH, then S can be solved by
A S4  B S3  C S2  D S  E  0
55
Theoretical Modeling
A
B
FO2 S 0O2
NS
FH 2 S 0 H 2
C 8
2
[4c2  16(1 
2
NS
FO2 S0O2
NS
[8c2  64(1 
c 2 16(
D  16(
2
FH 2 S 0 H 2
NS
FO S 0O
c2
c
2
)c1c2 ]  64 2 2 [(1  2 )c1c2  16c2 ]
c3
NS
c3
FH 2 S0 H 2
NS
c2
c
2
2
)c1c2  4c1 c2  128(1  2 ) 2 c1 ]
c3
c3
) 2 (1 
) 2 (1 
FH S0 H 2
c2
)   4 2 2 c2
c3
NS
c2
) c2
c3
E 0
i can be obtained by the isotherm
i 
56
H i  H S
)
kT
H i  H S
  S exp(
)]
kT
 S exp(
[1   S
Comparisons with Experiments
The experimental result shows
good agreements with theoretical
data especially at lower hydrogen
partial pressure regime.
Under higher hydrogen partial
pressures, the interface coverage i
saturates and deviates from the
predict behaviors.
This indicates that the i is
decreased with elevating the
temperature under the same
hydrogen partial pressure. As the i
becomes high enough then the Hi
decreases to Hb which results in
the accumulation of hydrogen
atoms at the Pd bulk.
57
Summary
The hydrogen sensing performances of Pd- and Pt-InGaP MOS
Schottky diodes have been systematically studied and compared under
steady-state condition at different temperature.
The Pd-InGaP Schottky diode exhibits large current variation and
change of barrier height under low hydrogen concentration ambient.
The Pt-InGaP Schottky diode shows better
performances and larger hydrogen detection regimes.
high-temperature
The initial heat of adsorption of Pd- and Pt-InGaP Schottky diodes are
355 and 364.8meV/atom, respectively.
Based on the Temkin isotherm model, the experimental results of
hydrogen coverage i are consistent with theroretical data over three
order of magnitudes of hydrogen partial pressure.
58
A High Electron Mobility Transistor
(HEMT) hydrogen Sensor with a
Pt-Oxide- Al0.24Ga0.76As MOS Structure
59
59
HEMT Device Structure and Process
Au/Ge/Ni
600Å GaAs
cap layer
Au/Ge/Ni
Pt
n+ = 2x1018 cm-3
oxide layer
δ(n+) = 4x1012 cm-2
200Å Al0.24Ga0.76As Schottky layer (n=3x1017 cm-3)
Gate
45Å undoped Al0.24Ga0.76As spacer
Drain
150Å undoped In0.15Ga0.85As channel layer
Source
5000Å undoped GaAs buffer
Gate Pad
S.I. GaAs substrate
05-05-21
60
Current-Voltage Characteristics
Drain Current ID (mA)
6
7
o
air
T=30
C
14ppm H2/air
2
AG=1.4x100m
98ppm H2/air
980ppm H2/air
VGS=0V
9970ppm H2/air
VGS=-0.3/step
6
Drain Current ID (mA)
7
5
o
air
T=160 C
14ppm H2/air
2
AG=1.4x100m
98ppm H2/air
VGS=0V
980ppm H2/air
9970ppm H2/air
5
4
4
3
3
2
VGS=-0.3V
2
VGS=-0.3V
1
1
VGS=-0.6V
VGS=-0.6V
VGS=-0.9V
0
0.0
0
0.5
1.0
1.5
2.0
Drain-Source Voltage VDS (V)
I DS 
61
VGS=-0.3/step
 nWG C
2 LG
0.0
0.5
1.0
1.5
Drain-Source Voltage VDS (V)
VGS  Vth 2
2.0
Drain Saturation Current Sensitivity
SJ (A/mm-ppm H2/air)
Drain Saturation Current Sensitivity
SJ
VGS = 0V & VDS = 1.2V
10
SJ 
10
10
1
J DS ,H 2  J DS ,air
CH2
0
o
30 C
o
72 C
o
112 C
o
160 C
-1
10
100
1000
10000
Hydrogen Concentration (ppm H2/air)
Hydrogen concentration ↑ → SJ ↓ → Current Variation Saturation
T ↑ → SJ ↓ → Low Hydrogen Concentration Limitation↑
62
Transconductance gm (mS/mm)
250
250
200
200
150
150
100
100
o
T = 30 C
50
air
14ppm H2/air
98ppm H2/air
980ppm H2/air
9970ppm H2/air
VDS = 1.2V
0
-1.5
-1.0
-0.5
0.0
0.5
Gate-Source Voltage VGS (V)
63
1.0
50
0
Drain Saturation Current ID (mA/mm)
gm & IDS V.S. VGS
gm
decay
120
90
60
Drain Saturation Current Variation IDS (A)
Threshold Voltage Shift Vth (mV)
Vth &  IDS V.S. CH2
10
-3
10
-4
VDS=1.2V & VGS=0V
Leakage current
o
10
30 C
o
72 C
o
112 C
o
160 C
-5
10
100
1000
10000
Hydrogen Concentration (ppm H2/air)
o
30 C
o
72 C
o
112 C
o
160 C
30
0
10
100
1000
10000
Hydrogen Concentration (ppm H2/air)
Hydrogen concentration ↑ → ∆Vth ↑ Linear relation with ln(CH2)
T ↑ → ∆Vth ↓
64
-2
Interface Adsorbed Site ni (cm )
Hydrogen Adsorbed Sites
10
~10%
13
~70%
~80%
10
10
12
14ppm H2/air
98ppm H2/air
494ppm H2/air
980ppm H2/air
9970ppm H2/air
11
20
40
60
80
100
120
o
Temperature ( C)
T ↑ → Interface adsorption sites ↓
65
140
160
p  ni
V 
s
Langmuir Adsorption Model Analysis
Inverse Threshold Voltage Shift
-1
1 / Vtn (V )
120
100
80
60
o
30 C
o
52 C
o
72 C
40
20
0.5
1.0
1.5
2.0
2.5
3.0
3.5
Inverse Square Root of Hydrogen Partial Pressure
-0.5
-0.5
PH (Torr )
2
66
0.25


P
1
1  O2
1

 0.5



Vth PH 2  K e  Vth,max  Vth,max
Van’t Hoff Equation Analysis
Logarithmic Value of
Equilibrium Constant ln Ke
0.4
o
o
52 C
30 C
0.3
0.2
o
72 C
-1
Slope = 0.50135 (K )
Intercept = -1.24201
0.1
2.9
3.0
3.1
3.2
3.3
Inverse Absolute Temperature 1000/T (1/K)
67
Van’t Hoff
equation
 H 0 S 0
ln K e 

RT
R
Ho (MOS) =-8.32KJ/mole
Transient Response V.S. Temperature
Drain Current ID (mA)
9970ppm H2/air
VDS = 1.2V
VGS = -0.3V
1.8
Oxygen
effect
1.6
1.4
o
72 C
o
o
1.2
30 C
o
112 C
1.0
H2 on
H2 off
0.8
0
5
10
15
20
25
Response Time (1000 sec)
T ↑ → a↓ Higher H2 dissociation rate
68
160 C
30
35
Transient Response Comparison
69
AlGaAs-Based
τa (sec)
Pt MOS HEMT
135
Pt MOS Schottky
296
Pt MS Schottky
330
Gray system
For given data sequence {x(k )  0, for 1  k  K}
x (1) ( k ) is found by 1-AGO as
k
x (1) (k ) = ∑x(n) (1)
n =1
1  k  K,where the
x (1) (1) = x(1),
 for
from(1),it is easy to recover x (1) (k ) as
x(k )  x (1) (k ) - x (1) (k  1) (2)
This operation is called 1-IAGO
70
Gray system
By x(k ) and x (1) ( k ) ,a gray difference
equation is fourmed as
where
and
x(k ) + az (1) (k ) = b(3)
z (1) (k ) = 0.5[ x (1) (k ) + x (1) (k 1)](4)
1
a
T
[ ] = ( B B) BT y  (5)
b
71
Gray system
where
 z (0)
 (0)
z
B

 (0)
 z
(2) 1

(3) 1



(k ) 1
and
 x (0)
 (0)
x

y
 
 (0)
 x
( 2) 

(3) 


(k )
the x (1) (k ) can solve as
b
x (k )  ( x(1)  )e
a
(1)
72
a ( k 1)
b
  (6)
a
Gray system
The estimate of x(k ) , xˆ (k ) ,is then
obtained by 1-IAGO as
xˆ (k )  x (1) (k ) - x (1) (k  1) (7)
 The GM (1,1) model is simple, and
sample less.
 However, the disadvantage is only
apply to less information .
73
GM(1,1) Model
原始序列X(0)(k)，求出累
加生成序列X(1)(k)
建立一階差分方程式
接著透過矩陣B與矩陣y
求出發展係數a和b
求一階差分方程式之通解
進行一次反累加生成，
求出建模後序列
The flow of GM(1,1) modeling
74
Gray system
40
35
1-AGO Process
Origin Data
30
Data
25
20
15
10
5
0
0
2
4
6
8
10
Value
The compare of origin data and 1-AGO process.
75
GPM Model
Since the measured hydrogen sensing data is a
series of non-negative sequence, we assume that
data.
Then the preprocess by 1-AGO is used and the
hydrogen series data could be obtained as:
k
(1)

(1)
D  { i1 D(i), 1  k  3}
Substitute (1) into 2-degree polynomial equation,
one can obtain that
 D (1) (k )  ak 2  bk  c, for1  k  3 (2)

76
GPM Model
The coefficient of the 2-degree polynomial equation, i.e.,
a, b, and c, in (2) could be found from the matrix as:
(1)
a   D (1)  1 1 1
b    D (1) (2) 4 2 1

  

(
1
)
 c   D (3)  9 3 1
1
(3)
Finally, the output developed grey hydrogen sensing
model, based on first-order inverse accumulated
generating operation (1-IAGO), could be presented
as:
^
^ (1)
D (k + 1)  D
77
^ (1)
(k + 1) - D
(k)
(4)
GPM Model
78
GPDM Model
79
80
Design of gas sensing micro-system
The proposed gas sensing micro-system.
81
Gas Sensor Device
Interface of sensor device(top view)
Sensing electrode(layer2)
Sensing area(layer1)
Heater(layer3)
82
Gas Sensor Device
Integrated gas sensor
Sensing area
Sensing array
Sensing electrode
Heater
Analysis circuit
Float structure
Si -sub
83
Device Fabrication
 The SEM picture of the sensor arrays (before catalytic
metal deposition)
84
Device Fabrication
 The SEM picture of the sensor (after catalytic metal
deposition)
85
Device Fabrication
Microphotograph of the sensor array
86
IC Microphotograph
Microphotograph of the sensor chip
87
Experimental Results and Discussion
 The typical output current-voltage (I-V) characteristics of the
studied device under air and 1% H2/air hydrogen gas at 25℃.
-3
2.0x10
H2(1%)
-3
Sensing output(A)
1.5x10
AIR
-3
1.0x10
-4
5.0x10
0.0
-4
-5.0x10
-0.2
0.0
0.2
0.4
0.6
0.8
Voltage(v)
88
88
Experimental Results and Discussion
 The measured hydrogen sensing response of 1% H2/air extract
from sensor device.
感測訊號
輸出訊號
89
89
Detecting system
Input Transducer
SENSORS
AMP
Signal Processing
MIX
ADC
DAC
Output Transducer
DEMIX
DRIVE
MICRO COMPUTER CONTROL
DIGITAL SIGNAL PROCESSING/ SECONDARY
PARAMETER COMPENSATION/DATA HANDING
90
ACTUATORS
MSC-51 硬體部分
 主要元件
• LCD
• ADC0804
 藍芽 (BC04)
96、98、99年度教育部產學計畫案
91
Circuit schematic
+5V
MCS-51
+5V
40
10uF
31
9
VCC
EA/VP
RESET
10K
30P
12MHZ
19
18
X1
X2
30P 20
VSS
16
17
13
WR
RD
INT0
74LS139
P10
P11
P12
P13
P14
P15
P16
P17
1
2
3
4
5
6
7
8
P00
P01
P02
P03
P04
P05
P06
P07
39
38
37
36
35
34
33
32
P1.4 2
P1.5 3
P1.0
P1.1
P1.2
P1.3
A
B
7
1
2
6
A
B
C
D
3
4
5
LT
BI/RBO
RBI
74LS47
Q1
4
5
6
7
Y0
Y1
Y2
E Y3
1
Q2
Q3
Q4
10KX4
a
b
c
d
e
f
g
2907X4
D0
D1
千位
百位
D2
D3
十位
個位
13
12
11
10
9
15
14
220X7
+5V
DOT
+5V
解析度為0.02V
220
20
P0.0 18
P0.1 17
P0.2 16
P0.3 15
P0.4 14
P0.5 13
P0.6 12
P0.7 11
5
1
2
3
DB0 (LSB) VCC Vin(+) 6
DB1
DB2
Vin(-) 7
DB3
DB4
DB5
A-GND 8
DB6
DB7 (MSB)
Vref/2 9
INTR
CLK-R 19
CS
RD
WR
GND CLK-IN 4
10
VR5K
+5V
2K
2.55V
3.9V
VR10K
10K
ADC0804
150pF
92
Portable Hydrogen Detector(96)
The portable hydrogen detector
miniature. The LCD display shows
the hydrogen concentration of
15ppm and the related voltage is
1.196V.
93
The portable hydrogen detector
miniature. The LCD display shows the
hydrogen concentration of 200ppm
and the related voltage is 3.0V.
98 project
Hydrogen
Sensing
Client
Server
bluetooth
bluetooth
chip
MSC-51
alarm
LCD display
94
98 project
95
99 project
96
99 project
97
98
99
100
致謝
特別感謝成功大學劉文超特聘教授的指導與鼓勵
感謝劉文超教授、陳慧英教授帶領之研究團隊
感謝國科會以及教育部經費補助
感謝CIC、NDL以及NCHC
感謝一路上幫助坤緯的朋友、同事以及學生們
謝謝聆聽
101