Chapter 3 Experiment and Measurement
3.3 Measurement system
3.3.2 Current-Voltage (I-V) measurement set-up with Drift
condition, it can find the characteristics of pH-ISFET. It can find the pH sensitivity from IDS-VGS curve of maximum transconductance. Beside, we can see that with different buffer solution the reference electrode voltage is shifted and shifted voltage per pH value is sensitivity, shown in Fig.3-3.
3.3.2 Current-Voltage (I-V) measurement set-up with drift
In order to measure drift phenomenon of pH-ISFETs with the same buffer solution and the same condition samples period of seconds, minutes and hours. After seven hours, we can compare drift phenomenon of all samples. This detection principle is in a similar manner to that of the pH measurement and is shown in Fig.3-4.
3.4 References
[1] Paik-Kyun Shin,”The pH-sensing and light-induced drift properties of titanium dioxide thin films deposited by MOCVD”, Applied Surface Science, vol. 214, pp.214-221, 2000.
Chapter 4
Results and Discussions
4.1 Introduction
This experiment use a high polymer, it is a hydrophobic material which can reduce H ion in a large number, the shortage is vulnerable to buffer solution in the sensing film, so we utilize a way that Nafion entrapment PR to produce REFET(Reference Electrode Field Effect Transistor). Since Nafion is a proton exchange membrane, it can protect PR for this feature and it become the mechanism of proton exchange to make ion absorb on the surface of PR steadily in fear of peel for the attack of buffer solution in a short time. This experiment discusses a best REFET (Reference Electrode Field Effect Transistor) in different structure and in various viewpoints.
4.2 Comparison of different structure’s feature
The experiment utilizes different approach of entrapment to measure the comparison of its structure’s feature. It use ZrO2/PR/Nafion and ZrO2-mix(PR+Nafion) two different structure’s approach of entrapment, and get the common conclusion that sensitivity of both reduce from 56mV/p in ZrO2 sensing layer to 5mV/pH and 8.3mV/pH(Fig 4-2)(Fig4-3).
The main reason is the entrapment PR (FH6400) can reduce the sensitivity efficiently, and it can get different material’s site-binding from Gouy-Chapman-Stern
Theory model[2] and Site-binding model[3], which traps the number of ion are also different. In addition, ZrO2[4] is the material of high K and the sensitivity of metal oxide to H ion is higher, and PR is a PVC high polymer material that is not easy to absorb H ion, so it higher than ψPR in
ZrO2
ψ , the sensitivity can reduce largely about 85%.
However, the performance of two structure on Drift since structure of ZrO2/PR/Nafion inferior to the structure of PR mix Nafion (Fig.4-5) (Fig.4-6)(Fig.4-7), buffer solution trough Nafion make the surface area that ions absorb to PR larger than the surface area of mingle one from the analysis of triple structure, and if uncovered PR immerse in buffer solution directly, it will easy to peel by the attack of solution quickly. Hence, the main reason that tripe layer structure is not stable as the mix one is the surface area of PR molecule contact with buffer solution larger than the surface area of mix one, so it is easy to attack by buffer solution.
4-3 The comparison of PR-mix-Nafion deposition on different structure
The comparison of this experiment utilize two different base on different Sensing film, ZrO2 and SiO2(Fig.4-8), and the material of both of them mix PR and Nafion coast on sensing film to get the sensitivity are 8.3mV/pH and 13.3mV/pH respectively.
The sensitivity measured in previously ZrO2 and SiO2 experiment are about 55mV/pH and 32.5mV/pH(Fig.4-3)(Fig.4-9). It concludes from site-binding model[1]
and experiment data that the main reason affect sensitivity is ” hydrophobic” from PR material cause H+ ions uneasy to absorb, so the H ion mainly absorb on the surface of PR and it not connect with the sensing layer in bottom. Nevertheless, the structure
base on SiO2 is inferior to ZrO2 on the improvement of sensitivity and stability of drift (Fig.4-10),it perhaps because interface of SiO2 and PR is not as well as the interface of ZrO2 and PR.
4-4 The comparison of different PR-mix-Nafion proportion’s feature
This experiment utilize PR mix Nafion in different proportion, there are concentration 5：1 and 1：1 on sensing-layer entrapment ZrO2. Among the result that 0.01ml PR mix 0.01ml Nafion entrapment ZrO2, it can observe the sensitivity from the 54.16mV/pH in the begging reduce to 8.3mV/pH(Fig.4-3), the other is the result that 0.05ml PR mix 0.01ml Nafion entrapment ZrO2 reduce from 54.16mV/pHr to 4.16mV/pH(Fig.4-13). From this phenomena, it can detect the concentration of PR affect directly to the sensitivity of REFET and it further prove PR is the main reason of reducing sensitivity in 4-3.
The performance of Drift (Fig.4-6)(Fig.4-14) can get the two sample’s stability (PR1:Nafion1) is superior to (PR5:Nafion1) in the four hours later, the possible cause from the proportion of Nafion of the former higher than the later one. It mean the PR area entrap Nafion larger than the later, so it is uneasy to attack by the solution and cause PR peeling. In conclude, the sensitivity in (PR5:Nafion1) (Fig.4-15) is small and the time for stable of reliability is short, an the other vice versa.
4-5 The comparison of different proportion’s durability and repeatability
This experiment utilizes two structures in 4-4 (Fig.4-12) continue to do long time durability test, the first stage is measure sensitivity by doing four hours DRIFT
experiment to the measured sample respectively, and the second stage repeat the first stage experiment again. In this research, it observed the experiment of the structure can’t bear doing long term measure immersed the solution, and the feature of sensitivity and drift measured in the four hours can be made as a REFET(Reference Electrode Field Effect Transistor). Also, it observed that the feature of the two kind of mix proportion on sensitivity and drift in the measure of second stage already peel almost wholly for the long time attack in the buffer solution to make the mixing layer of PR and Nafion of the sample be invalid. It is realized in this experiment the only fine REFET (Reference Electrode Field Effect Transistor) of the structure in the four hours short time is unappreciable to do the long time measure.
4.6 Conclusion
To integrate the above experiment result, the mix layer of Nafion and PR is a good (Reference Electrode Field Effect Transistor), it could reduce H+ Sensitivity from 57.5mV/pH to 8mV/pH. It use easy approach of entrapment to make Nafion do for the entrapped PR steadily through the mechanism of proton exchange, and it observed in the experiment the OXIDE and ZrO2 of the bottom of PR is not associated directly with the SENSITIVITY, the main effect reason is PR which is not easy for the absorbing of H ion.
4.7 References
[1] John Payne ”Nafion® - Perfluorosulfonate Ionomer”, April, 2005 from http://www.psrc.usm.edu/mauritz/nafion.html
[2] R.E.G. van Hal et al. , “A general model to describe the electrostatic potential at
electrolyte oxide interface”, Advance in Colloid and Interface Science, vol.69, pp.31-62, 1996
[3] 吳浩青, 李永舫, ”電化學動力學”, 科技圖書公司, 2001 年 2 月
[4] K. M. Chang, K. Y. Chao, T. W. Chou, and C. T. Chang, ”Characteristics of Zirconium Oxide Gate Ion-sensitive Field-Effect Transistors” Japanese Journal of Applied Physics Vol. 46 No. 7A pp. 4334-4338 2007.
Chapter 5 Future work
From this experiment, it can realize that use the deposition feature of Nafion to entrap material of PR on a good sensing film and it get the feature of PR from the teat result. It can utilize the approach of entrapment to combine other substance (like protein, enzyme…etc) in the future, and ISFET develop BIO-SENSOR in further.
Source Drain Reference
electrode
Fig. 1-1 ISFET Cross-Section Structure
Sensing membrane Test range(pH) Sensitivity(mV/pH) Reference
ZrO2 1-13 57.5 2
Si3N4 1-13 46-56 3
Al2O3 1-13 53-57 4
Ta2O5 1-13 56-57 5
SnO2 2-10 58 3
Table 1-1 Sensitivities and test range for different sensing membranes.
Fig. 1-2 important platform of Bio-sensors
Fig.1-3 electrode structure
Fig. 1-4 Conventional glass electrode
Fig. 1-5 using solid-state technology in measurement system
Source Drain
Reference electrode
Gate
Source Drain
MOSET ISFET Fig 2-1 Structure of MOSFET and ISFET
Fig 2-2 Site-binding model
Fig.2-3 Silicon dioxide and electrolyte interface
Fig.2-4 Potential profile and charge distribution at an oxide electrolyte solution interface.
Fig. 2-5 Gouy-Chapman-Stern model
silicon silicon
Thermal Oxide Thermal Oxide
Sensing Layer
Sensing Layer Hydration
Solution Solution
Fig.2-6 Series combination of the (a) initial (b) hydrated insulator capacitance
Step1
Step2
Step3
Step4
Step5
Step6
Step7
Step8
Setp9
Fig. 3-1 Fabrication Process Flow
parameters of ZrO2 sputter power : 110 W Ar / O2 : 24 / 8 ( sccm )
Density : 6.51 Acoustic impendance : 14.72
Tooling factor : 0.533 Rate : 0.01 Å / s pre sputter 60W for 10 min
Pressure : 7.6×10-3
Table 3-1 ZrO2 Sputtering parameters
Dark Box
Drain2 Drain1 Source
V
DS2V
DS1V
GSGate
Fig 3-2 Measurement set-up
0.0 0.5 1.0 1.5 2.0 2.5 3.0 1.1
1.2 1.3 1.4 1.5 1.6
ZrO2
H+ Sensitivity = 57.89 mV/pH
IDS (mA)
VG (V)
pH = 13 pH = 5 pH = 11 pH = 3 pH = 9 pH = 1 pH = 7
Fig 3-3 Extraction method of sensitivity
7
Fig 3-4 Extraction method of drift
Fig.4-1 The comparison between enclosure and entrapment
-0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
Fig.4-2 The variety of ZrO2 sensitivity to H+after coated with PR/Nafion
-0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
Fig. 4-3 The variety of ZrO2 H+ sensitivity after coated with PR :Nafion=1:1
Fig. 4-4 The comparison of surface potential between ZrO2 and SiO2
-2000 0 2000 4000 6000 8000 10000 12000 14000 16000 for first hour to fourth hour
0.346V
Fig4-5 Time to drift in pH buffer solution of ZrO2/PR/Nafion-REFET for 4 hours
-2000 0 2000 4000 6000 8000 10000 12000 14000 16000 1.50
Drift in pH buffersolution for first hour to fourth hour
ZrO2-mix(PR1:Nafion1)
Fig4-6 Time to drift in pH buffer solution of ZrO2-mix(PR1:Nafion1)-REFET for 4 hours
1.0 1.5 2.0 2.5 3.0 3.5 4.0 0
50 100 150 200 250 300 350
VG (mV)
Time (hour) ZrO2/PR/Nafion ZrO2-mix(PR1:Nafion)
Fig4-7 The drift phenomenon in different structure
Fig.4-8 Compare in different sensing-layer
Fig. 4-9 The variety of SiO2 H+ sensitivity after coated with PR and Nafion
-2000 0 2000 4000 6000 8000 10000 12000 14000 16000 1.6
1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6
VG (V)
Time (s) Drift in pH buffer solution for first hour to fourth hour
0.529V
Fig4-10 Time to drift in pH buffer solution of SiO2-mix(PR1:Nafion1)-REFET for 4 hours
1.0 1.5 2.0 2.5 3.0 3.5 4.0 0
100 200 300 400 500 600
VG (V)
Time (hour) ZrO2-mix(PR+Nafion) SiO2-mix(PR+Nafion)
Fig4-11 The drift phenomenon in different sensing-layer
Fig4-12 The comparison between different proportions of PR and Nafion
Fig4-13 The variety of SiO2 H+ sensitivity after coating with PR:Nafion=5:1
-2000 0 2000 4000 6000 8000 10000 12000 14000 16000 1.600
1.625 1.650 1.675 1.700 1.725 1.750
VG (V)
Time (s)
20.20mV
Drift in pH solution for first hour to fourth hour ZrO2-mix(PR5:Nafion1)
Fig4-14 Time to drift in pH buffer solution of ZrO2-mix(PR5:Nafion1)-REFET for 4 hours
1.0 1.5 2.0 2.5 3.0 3.5 4.0 0
2 4 6 8 10 12 14 16 18 20 22
VG (V)
Time (hour) ZrO2-mix(PR1:Nafion1) ZrO2-mix(PR5:Nafion1)
Fig4-15 The drift phenomenon in different proportions of PR:Nafion
Fig4-16 Sensitivity variety from 1st to 2nd measurement of ZrO2-mix(PR1:Nafion1)
Fig4-17 Sensitivity variety from 1st to 2nd measurement of ZrO2-mix(PR5:Nafion1)
0 2 4 6 8
0 10 20 30 40 50 60
Sensitivity(mV/pH)
Time(hour) ZrO2-mix(PR1:Nafion1) ZrO2-mix(PR5:Nafion1)
Fig4-18 The variety of sensitivity in 8 hours
Fig4-19 Drift variety from 1st to 2nd measurement of ZrO2-mix(PR1:Nafion1)
Fig4-20 Drift variety from 1st to 2nd measurement of ZrO2-mix(PR5:Nafion1)
0 1 2 3 4
Fig.4-21 Drift v.s. time in 4hours
4 5 6 7 8
簡歷
姓 名：陳 明 聰 性 別：男
出生日期：民國 69 年 2 月 29 日 出 生 地：台灣省台北縣
住 址：台北縣鶯歌鎮中正一路 475 號 學 歷：私立龍華科大學電機工程學系 (民國 88 年 9 月~民國 92 年 6 月)
國立交通大學微電子奈米科技產業研發碩士專班
(民國 95 年 2 月~民國 97 年 2 月)
碩士論文：以NafionTM/PR包埋結構作為參考場效電晶體之感測層研究
The study of NafionTM/PR entrapment structure as REFET Sensing film