Chapter 4 Results and Discussions
4.5 Conclusion
The pH sensing characteristics of zirconium dioxide gate pH-ISFET were investigated for various annealing temperature of 30 min duration in nitrogen. It is found that annealing temperature of 600℃ has a maximal sensitivity of 54.5 mV/pH.
Because of the sensing layer surface of 600℃ sample has a denser site.
We can find that the hysteresis width of 600℃ sample in pH loop 7-3-7-11-7 is 1.43 mV, and the hysteresis in pH loop 7-11-7-3-7 is 5.45 mV. It can be observed that hysteresis in the acid side is smaller than basic side, results in asymmetric hysteresis.
For the application of the pH measurement, the maximum hysteresis of 600℃ sample is 5.45mV. It occupies 10％ of pH-sensitivity. The error causes by hysteresis can be accepted in pH measurement.
The drift rate of the ZrO2 gate pH-ISFET for not annealing and annealing temperature at 600, 700, 800, 900 ℃ are 2.4, 0.54, 1.9, 1.76 and 1.0 mV/h, respectively. Since the sensing layer surface of 600℃ sample has a denser site, it is relatively difficult to generate the hydrated layer. Therefore, annealing temperature at 600℃ shows the smallest drift rate.
In order to achieve the purposes for high pH-sensitivity, small hysteresis and low
drift. We can conclude the optimal annealing temperature is around 600℃. It reveals that ZrO2 gate pH-ISFET annealed at 600℃ is suitable for pH measurement.
4.6 References
[1] T. Mikolajick, Feldeffekttransistoren zur pH-Wert-Messung undals transducer fur Biosensoren, Thesis, University of Erlangen Nuremberg, 1996.
[2] L. Bousse, S. Mostarshed, B.van der schoot, N.F. de Rooij, Comparison of the hysteresis of Ta2O5 and Si3N4 pH-sensing insulators, Sens. Actuat. B 17 (1994) 157-164.
[3] L. Bousse, P. Bergveld, The role of buried OH－ sites in the response mechanism of inorganic-gate pH-sensitive ISFETs, Sens. Actuat. 6 (1984) 65–78.
[4] Y. Zhong, S. Oho and T. Lin: Chinese J. Semicond. 12 (1994) 838.
[5] Z. Yule, Z. Shouan, L. Tao, Drift characteristic of pH-ISFET output, Chin. J.
Semicond. 12 (15) (1994) 838-843.
[6] S. Jamasb, S. Collins, R. L. Smith, A physical model for drift in pH ISFETs, Sens.
Actuat. B 49 (1998) 146-155.
Chapter 5 Future work
In this study, an optimum annealing condition for ZrO2 gate pH-ISFET was investigated. The annealing temperature at 600 ℃ shows the higher sensitivity, smaller hysteresis and lower drift than others. Further investigation is attained to improve the pH-sensitivity properties. It can be achieved by optimizing the deposition condition, and regard to crystallographic properties of the sensing films and oxygen migration in the sensing film. In addition, we can anneal at different times to find out the properties of sensing film.
MOSFET ISFET
Fig. 1-1 Structure of MOSFET and ISFET
Fig. 1-2 Conventional glass electrode Gate
Source Drain
Source Drain
Reference electrode
Glass Membrane Internal Reference Electrode Internal
Buffer Solution
Internal Conducting Line
Fig. 2-1 Site-binding model
Fig. 2-2 Potential profile and charge distribution at an oxide electrolyte solution interface
(a) (b)
Figure 2-3 Series combination of the (a) initial (b) hydrated insulator capacitance
(a)
Silicon
Thermal Oxide Sensing Layer Solution
Hydration
(b)
(c)
(d)
(e)
(f)
(g)
Fig. 3-1 Fabrication process flow
Fig. 3-2 Measurement setup
Fig. 3-3 Extraction method of sensitivity
0 2 4 6 8 10 12 14 16 2
4 6 8 10 12
pH
Time (min)
Fig. 3-4 Measuring step of the hysteresis curve
Fig. 3-5 Detection principle of drift
Fig. 4-1 Sensitivity characteristic of ZrO2 gate ISFET at 600℃ sample
Fig. 4-2 Linearity characteristic of ZrO2 gate ISFET at 600℃ sample
-0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
Fig. 4-3 Linearity characteristic of ZrO2 gate ISFET at 700℃ sample
Fig. 4-4 Linearity characteristic of ZrO2 gate ISFET at 800℃ sample
0 2 4 6 8 10 12 14
Fig. 4-5 Linearity characteristic of ZrO2 gate ISFET at 900℃ sample
Fig. 4-6 Sensitivity characteristic of ZrO2 gate ISFET at 700℃ sample
0 2 4 6 8 10 12 14
Fig. 4-7 Sensitivity characteristic of ZrO2 gate ISFET at 800℃ sample
Fig. 4-8 Sensitivity characteristic of ZrO2 gate ISFET at 900℃ sample
-0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
Fig. 4-9 Sensitivity characteristic of ZrO2 gate ISFET at not annealed sample
Fig. 4-10 Linearity characteristic of ZrO2 gate ISFET at not annealed sample
-0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
Fig. 4-11 SEM image of ZrO2 gate ISFET at not annealed sample
Fig. 4-12 SEM image of ZrO2 gate ISFET at 600℃ sample
Fig. 4-13 SEM image of ZrO2 gate ISFET at 700℃ sample
Fig. 4-14 SEM image of ZrO2 gate ISFET at 800℃ sample
Fig. 4-15 SEM image of ZrO2 gate ISFET at 900℃ sample
Fig. 4-16 The pH sensitivity of ZrO2 gate pH-ISFET annealed at different temperature
30 35 40 45 50 55 60
not annealed
600℃ 700℃ 800℃ 900℃
Sen sitiv ity (m V/p H)
Fig. 4-17 Hysteresis curves of ZrO2 gate ISFET at pH loop 7-3-7-11-7 to 600℃ sample
Fig. 4-18 Hysteresis curves of ZrO2 gate ISFET at pH loop 7-3-7-11-7 to 700℃ sample
1 2 3 4 5 6 7 8 9 10 11 12 13
1.6 1.7 1.8 1.9 2.0 2.1
VG = 1.43 mV
VG(V)
pH Value
1 2 3 4 5 6 7 8 9 10 11 12 13
1.25 1.30 1.35 1.40 1.45 1.50 1.55 1.60
VG = -12.52 mV
VG(V)
pH Value
Fig. 4-19 Hysteresis curves of ZrO2 gate ISFET at pH loop 7-3-7-11-7 to 800℃ sample
Fig. 4-20 Hysteresis curves of ZrO2 gate ISFET at pH loop 7-3-7-11-7 to 900℃ sample
1 2 3 4 5 6 7 8 9 10 11 12 13
1.7 1.8 1.9 2.0 2.1
VG = 4.46 mV
VG(V)
pH Value
1 2 3 4 5 6 7 8 9 10 11 12 13
1.3 1.4 1.5 1.6 1.7
VG = 53 mV
VG(V)
pH Value
Fig. 4-21 Hysteresis curves of ZrO2 gate ISFET at pH loop 7-3-7-11-7 to not annealed sample
Fig. 4-22 Hysteresis curves of ZrO2 gate ISFET at pH loop 7-11-7-3-7 to 600℃ sample
1 2 3 4 5 6 7 8 9 10 11 12 13
1.6 1.7 1.8 1.9 2.0
VG = -6.36 mV
VG(V)
pH Value
1 2 3 4 5 6 7 8 9 10 11 12 13
1.6 1.7 1.8 1.9 2.0 2.1
VG = 5.45 mV
VG(V)
pH Value
Fig. 4-23 Hysteresis curves of ZrO2 gate ISFET at pH loop 7-11-7-3-7 to 700℃ sample
Fig. 4-24 Hysteresis curves of ZrO2 gate ISFET at pH loop 7-11-7-3-7 to 800℃ sample
1 2 3 4 5 6 7 8 9 10 11 12 13
1.7 1.8 1.9 2.0 2.1
VG = 8.23 mV
VG(V)
pH Value
1 2 3 4 5 6 7 8 9 10 11 12 13
1.30 1.35 1.40 1.45 1.50 1.55 1.60
VG = 22.27 mV
VG(V)
pH Value
Fig. 4-25 Hysteresis curves of ZrO2 gate ISFET at pH loop 7-11-7-3-7 to 900℃ sample
Fig. 4-26 Hysteresis curves of ZrO2 gate ISFET at pH loop 7-11-7-3-7 to not annealed sample
1 2 3 4 5 6 7 8 9 10 11 12 13
1.3 1.4 1.5 1.6 1.7
VG = 11.67 mV
VG(V)
pH Value
1 2 3 4 5 6 7 8 9 10 11 12 13
1.6 1.7 1.8 1.9 2.0
VG = 5.69 mV
VG(V)
pH Value
Fig. 4-27 Drift in pH 7 buffer solution of ZrO2 gate ISFET for 6 hours at 600℃ sample
Fig. 4-28 Drift in pH 7 buffer solution of ZrO2 gate ISFET for 6 hours at 700℃ sample
0 50 100 150 200 250 300 350 400 1.796
1.797 1.798 1.799 1.800 1.801
VG(V)
Time(mins)
Drift = 3.23mV
0 50 100 150 200 250 300 350 400 1.65
1.66 1.67 1.68 1.69 1.70 1.71
VG(V)
Time(mins)
Drift = 11.38mV
Fig. 4-29 Drift in pH 7 buffer solution of ZrO2 gate ISFET for 6 hours at 800℃ sample
Fig. 4-30 Drift in pH 7 buffer solution of ZrO2 gate ISFET for 6 hours at 900℃ sample
0 50 100 150 200 250 300 350 400 1.868
1.870 1.872 1.874 1.876 1.878 1.880 1.882 1.884
VG(V)
Time(mins)
Drift = 10.55mV
0 50 100 150 200 250 300 350 400 1.505
1.510 1.515 1.520 1.525
VG(V)
Time(mins)
Drift = 5.99mV
Fig. 4-31 Drift in pH 7 buffer solution of ZrO2 gate ISFET for 6 hours at not annealed sample
Table 3-1 Parameters of sensing layers deposition with Sputter
parameters of ZrO2 sputter power : 110 W
Ar / O2 : 24 / 8 ( sccm ) Density : 6.51
Acoustic impendance : 14.72 Tooling factor : 0.533
Rate : 0.02 Å / s pre sputter 60W for 10 min
Pressure : 7.6×10-3
0 50 100 150 200 250 300 350 400 1.86
1.87 1.88 1.89 1.90
VG(V)
Time(mins)
Drift = 14.4mV
Table 3-2 The different annealing condition of ZrO2 gate ISFET
Temperature (℃) Gas Time (min)
Not annealed N2 30
600 N2 30
700 N2 30
800 N2 30
900 N2 30
Table 4-1 The comparison of different test loop in hysteresis
Test loop Temperature
7 – 3 – 7 – 11 – 7 (mV)
7 – 11 – 7 – 3 – 7 (mV)
Not annealed -6.36 5.7
600℃ 1.43 5.45
700℃ -12.52 22.27
800℃ 4.46 8.23
900℃ 53 11.67
Table 4-2 Drift rate of ZrO2 gate ISFET at different annealing temperature
Temperature Drift rate (mV/h)
Not annealed 2.4
600℃ 0.54
700℃ 1.9
800℃ 1.76
900℃ 1.0
簡 歷
姓 名：詹秉燏 性 別：男
出生日期：民國 73 年 09 月 10 日 籍 貫：台灣省台中市
學 歷：國立彰化師範大學電機工程學系 國立交通大學電子工程研究所
碩士論文：二氧化鋯作為閘極之離子感測場效電晶體應用在 pH 量測之最佳化退火製程研究
The study of optimal annealing process for ZrO2 gate ISFETs in
pH measurement applications