Chapter 4 Results and Discussions
5.1 Future work
In the study, the method of improving the drift has already experimented.
Although we can make the drift be a constant by this method, but the constant is not zero. This situation is caused by the threshold voltage mismatch to n-type and p-type pH-ISFET. The threshold voltage can be adjusted by the ion implantation in, and then we must control the quality of pH-ISFET sensing film. Therefore, the drift can be eliminated through the optimum process and the compensative method, it will be suitable to the pH-ISFET in the future applications.
Figure 1-1 Schematic representation of the side-binding model
Figure 1-2 Schematic representation of the Helmholtz double layer model (a) The charge distribution (b) The potential distribution
Figure 1-3 Schematic representation of Gouy and Chapman model (a) The charge distribution (b) The potential distribution
Figure 1-4 Schematic representation of Gouy – Chapman – Stern model (a) The charge distribution (b) The potential distribution
(a) (b)
Figure 2-1 Schematic representation of(a) MOSFET, (b) ISFET
Figure 2-2 Potential profile and charge distribution at an oxide electrolyte solution interface
Drain Source Gate
electrolyte
Figure 2-3 Series combination of the (a) initial (b) hydrated insulator capacitance
(a)
(b)
Substrate
Substrate
Silicon
Thermal Oxide Sensing Layer Solution
Hydration
(c)
(d)
(e)
Substrate
S D
D
Substrate
Substrate
(f)
(g)
Substrate
S D
D
Substrate
S D
D
(h)
(i)
Substrate
S D
D
Substrate
S D
D
(j)
(k)
Figure 3-1 Fabrication process flow
Substrate
S D
D
Substrate
S D
D
Figure 3-2 Measurement setup
Figure 3-3 Detection principle of pH
Gate
Drain1 Source Drain2
V
GSV
DS1V
DS2Figure 3-4 Detection principle of drift
0.0 0.5 1.0 1.5 2.0 2.5 3.0 Figure 4-1 Id-Vg curve of ZrO2 to n-type ISFET before drift
0 2 4 6 8 10 12 14 Figure 4-2 Sensitivity characteristic of ZrO2 to n-type ISFET before drift
-3 -2 -1 0 1
Figure 4-3 Id-Vg curve of ZrO2 to p-type ISFET before drift
0 2 4 6 8 10 12 14
Figure 4-4 Sensitivity characteristic of ZrO2 to p-type ISFET before drift
0.0 0.5 1.0 1.5 2.0 2.5 3.0
Figure 4-5 Id-Vg curve of ZrO2 to n-type ISFET after drift in pH7 buffer solution for 7 hours
0 2 4 6 8 10 12 14
Figure 4-6 Sensitivity characteristic of ZrO2 to n-type ISFET after drift in pH7 buffer solution for 7 hours
-3 -2 -1 0 1
Figure 4-7 Id-Vg curve of ZrO2 to p-type ISFET after drift in pH7 buffer solution for 7 hours
0 2 4 6 8 10 12 14
Figure 4-8 Sensitivity characteristic of ZrO2 to p-type ISFET after drift in pH7 buffer solution for 7 hours
0 2 4 6 8 10 12 14
Figure 4-9 Sensitivity characteristic of ZrO2 to n-type ISFET after drift in pH7 buffer solution 7 hours whose operation current is the same as original sensitivity
0 2 4 6 8 10 12 14
Figure 4-10 Sensitivity characteristic of ZrO2 to p-type ISFET after drift in pH7 buffer solution 7 hours whose operation current is the same as original sensitivity
0 5000 10000 15000 20000 25000 30000
drift in pH3 buffer solution for 7 hours
Figure 4-11 Time to drift in pH3 buffer solution of n-type ISFEET for 7 hours
0 5000 10000 15000 20000 25000 30000 1.53
drift in pH5 buffer solution for 7 hours
-51.54mV
VG(V)
Time(s)
Figure 4-12 Time to drift in pH5 buffer solution of n-type ISFEET for 7 hours
0 5000 10000 15000 20000 25000 30000 1.89
1.90 1.91 1.92 1.93 1.94 1.95
drift in pH7 buffer solution for 7 hours
VG(V)
Time(s)
-41.61mV
Figure 4-13 Time to drift in pH7 buffer solution of n-type ISFEET for 7 hours
0 5000 10000 15000 20000 25000 30000 1.58
1.59 1.60 1.61 1.62 1.63 1.64
drift in pH9 buffer solution for 7 hours
-34.66mV
VG(V)
Time(s)
Figure 4-14 Time to drift in pH9 buffer solution of n-type ISFEET for 7 hours
0 5000 10000 15000 20000 25000 30000 1.99
2.00 2.01 2.02 2.03 2.04 2.05
drift in pH11 buffer solution for 7 hours
-32.52mV
VG(V)
Time(s)
Figure 4-15 Time to drift in pH11 buffer solution of n-type ISFEET for 7 hours
2 4 6 8 10 12
-10 -9 -8 -7 -6 -5
y=0.57441-11.31647 R=0.98184
pH value
Drift rate(mV/h)
Figure 4-16 Time to drift rate of n-type ISFET in various buffer solution
0 5000 10000 15000 20000 25000 30000
drift in pH3 buffer solution for 7 hours
Figure 4-17 Time to drift in pH3 buffer solution of p-type ISFEET for 7 hours
0 5000 10000 15000 20000 25000 30000 -0.874
drift in pH5 buffer solution for 7 hours
6.04mV
Time(s)
VG(V)
Figure 4-18 Time to drift in pH5 buffer solution of p-type ISFEET for 7 hours
0 5000 10000 15000 20000 25000 30000 -0.864
-0.862 -0.860 -0.858 -0.856 -0.854 -0.852 -0.850 -0.848
drift in pH7 buffer solution for 7 hours
-4.91mV
Time(s)
VG(V)
Figure 4-19 Time to drift in pH7 buffer solution of p-type ISFEET for 7 hours
0 5000 10000 15000 20000 25000 30000 -0.90
-0.88 -0.86 -0.84 -0.82 -0.80
drift in pH11 buffer solution for 7 hours
25.92mV
VG(V)
Time(s)
Figure 4-20 Time to drift in pH9 buffer solution of p-type ISFEET for 7 hours
0 5000 10000 15000 20000 25000 30000
drift in pH11 buffer solution for 7 hours
-30.82mV
VG(V)
Time(s)
Figure 4-21 Time to drift in pH11 buffer solution of p-type ISFET for 7 hours
2 4 6 8 10 12
Figure 4-22 Time to drift rate of p-type ISFET in various buffer solution
2 4 6 8 10 12
Figure 4-23 Time to drift of the compensation on the pH-ISFET in various buffer solution
Figure 4-24 Time to drift rate of the compensation on the pH-ISFET in various buffer solution
2 4 6 8 10 12
Figure 4-25 The comparison of drift between compensative drift and the original drift to the pH-ISFET in various buffer solution
0 2 4 6 8 10 12 14
Figure 4-26 The comparison of sensitivity between compensative sensitivity and the original sensitivity to the pH-ISFET
0 5 10 15 20 25 30
Figure 4-27 Hysteresis phenomenon to time of n-type pH-ISFET
0 5 10 15 20 25 30
pH7 pH7 pH7 pH7 pH7
pH13 pH13
VG(V)
Time(mins)
Figure 4-28 Hysteresis phenomenon to time of p-type pH-ISFET
0 5 10 15 20 25 30
Figure 4-29 Hysteresis phenomenon to time of n-type pH-ISFET after drift in pH7 buffer solution for 7 hours
0 5 10 15 20 25 30
Figure 4-30 Hysteresis phenomenon to time of p-type pH-ISFET after drift in pH7 buffer solution for 7 hours
Diameter (mm): 100+/-0.5 Diameter (mm): 100+/-0.5 Type / Dopant : P / Boron Type / Dopant : P / Phosphorous
Orientation : <100> Orientation : <100>
Resistivity (ohm-cm):1-10 Resistivity (ohm-cm):1-12 Thickness (μm) ：505-545 Thickness (μm) ：515545
Grade : Prime Grade : Prime
Table 3-1 (a) Specifications of wafers
parameters of ZrO2 sputter power : 200 W
Ar / O2 : 24 / 8 ( sccm ) Density : 6.51
Acoustic impendance : 14.72 Tooling factor : 0.533
Rate : 0.01 Å / s
pre sputter 60W for 10 min Pressure : 7.6×10-3
Table 3-1 (b) Specifications of wafers
Parameters of sensing layers deposition with Sputter
N-type pH-ISFET P-type pH-ISFET Original
sensitivity/
operation current
58.73mV/pH /
Table 4-1 Sensitivity at the optimum operation current
N-type pH-ISFET P-type pH-ISFET Original
sensitivity/
operation current
58.73 mV /pH /
Table 4-2 Sensitivity at the immobile operation current
N-type
Table 4-3 Total drift in different pH buffer solution for 6 hours
N-type
Table 4-4 Drift rate in different pH buffer solution for 6 hours
N-type
Sensitivity 58.73 mV/pH 57.9 mV/pH 57.08 mV/pH
Table 4-5 The comparison of the sensitivity
N-type
Table 4-6 The comparison of the sensitivity