Chapter 4 Results and Discussions
4.3 The coplanar ISFET/REFET sensor array system
The sensor array system is composed by the coupled sensing membrane without plasma treatment and with post-plasma-treatment after deposition. In this experiment, we use TiO2 membrane without and with NH3 post-plasma-treatment to form the ISFET/REFET sensor array system, and ZrO2 membrane without and with NH3
post-plasma-treatment as the ISFET/REFET sensor array system. Thus, the table 4.3 lists the difference of coplanar structure in TiO2 membrane and table 4.4 lists the difference of coplanar structure in ZrO2 membrane. Obviously, the difference of sensitivity increased with longer NH3 plasma treating time. The highest value we have about 34.2 mV/pH made by ZrO2 pair.
4.4 Conclusions
In this work, we are trying to study the influence factors with sensitivity and attending to simplify the manufacturing of REFET. For the further purpose, we are trying to realize the comanufacturing process of ISFET/REFET sensing array with compatible CMOS manufacturing process. And different from other gate materials of REFETs, the sensing materials are available in CMOS fabrication technology in this work. Fortunately, the purposed NH3 plasma surface treatment work for the purpose indeed. A novel fabrication of REFET with plasma surface treatments is demonstrated.
And we have the sensitivity of co-planar structure of ISFET/REFET are 30.8mV/pH by TiO2/NH3_plasma_treated_30mins_TiO2 and 34.2mV/pH by ZrO2/NH3_plasma_treated_60mins_ZrO2.
Chapter 5 Future work
5.1 Future work
We had introduced the method of co-manufacturing ISFET/REFET by plasma treatment successfully in this work. Most of the attempts to create a REFET are based on covering the gate oxide of an ISFET with an additional ion insensitive membrane.
Such as PVC membranes, but it is pity that they are not MOSFET fabrication compatible and the manufacturing of this material is complicated. So, the purposed methods of co-manufacturing ISFET/REFET are useful.
However, there still are lots of problems in ISFET. Such as the stability of sensing membrane, the reproducibility of ISFET (drift phenomenon ), and the minification of ISFET. The minfication of ISFET is purposed by taking the solid state electrode replace the huge reference electrode immersed in the electrolyte.
Finally, based on the knowledge of ion-sensitive field effect transistor, the ion-selective field effect transistor can be produced by the same MOSFET manufacturing process. The ion-selective field effect transistor, resulted from sensing specific ions with the specific membrane, is also a proper extensive topic for future study.
Diameter (mm): 100+/-0.5 Type / Dopant : P / Boron
Orientation : <100>
Resistivity (ohm-cm):1-10 Thickness (μm) ：505-545
Grade : Prime (a) Specifications of wafers
TiO2
Density 4.26 Z-ratio 0.4 Tooling 50.47 Current (mA) 1 ~ 60
Rate (Å/sec) 1.2 Pressure (Torr) 5*10-6
(b)
E – gunparameters 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 (c) Sputter
NH3
Pressure=200mtorr RF power=100w Flow rate=30sccm Temperature=300℃
(d) Plasma
Table 3.1 (a) Specifications of wafers
(b) Parameters of sensing layers deposition with E – gun (c) Parameters of sensing layers deposition with Sputter
(d) Condition of plasma treatment
Sensitivity (mV/pH) 1~7 7~13 1~13
0 min 58.3 53.3 55.8
5 mins 61.7 41.7 51.7
10 mins 55 20 61.7
20 mins 40 25 32.5
30 mins 28.3 16.7 22.5
TiO2_NH3 plasma treatment
60 mins 30 30 30
Table 4.1 Sensitivity values of TiO2 with NH3 plasma treatment during time interval
Sensitivity (mV/pH) 1~7 7~13 1~13
Table 4.2 Sensitivity values of ZrO2 with NH3 plasma treatment during time interval
Sensitivity(mV/pH) 1~7 7~13 1~13
5 mins -3.4 11.6 4.1 Table 4.3 The sensitivity of coplanar structure in TiO2 membrane
Sensitivity(mV/pH) 1~7 7~13 1~13
5 mins 6.7 1.6 4.2 Table 4.4 The sensitivity of coplanar structure in ZrO2 membrane
Fig 1.1 The schematic of ISFET
Fig 2.1 ISFET structure band diagram (Luc Bousse, J. Chem. Phys. , 76 )
Figure 2.2 Potential profile and charge distribution at oxide / electrolyte interface
`
(a) RCA clean bare silicon
(b) wet oxidation
(c) maskⅠ
(d) screening oxidation & implantation
Figure 3.1 Experimental process
(e) passivation layer deposition
(f) maskⅡ& dryoxidation
(g) sensing layer α deposition
Figure 3.1 Experimental process
(i) Surface plasma treatment
(j) Sensing layer β deposition & mask Ⅲ
(k) Al deposition
Figure 3.1 Experimental process
Fig 4.1 I-V curves of TiO2 without plasma treatment Sensitivity_TiO2_PH=1-13
y = 0.057x + 1.4841 R2 = 0.998
0 0.5 1 1.5 2 2.5
0 2 4 6 8 10 12 14
ph
Vg
Fig 4.2 Sensitivity chart of TiO2 without plasma treatment
Fig 4.3 I-V curves of TiO2 membrane with NH3 plasma treatment during 5 minutes
Sensitivity_TiO2_NH3 plasma 5mins_PH=1-13
y = 0.0525x + 1.4796 R2 = 0.9902
0 0.5 1 1.5 2 2.5
0 2 4 6 8 10 12 14
ph
Vg
Fig 4.4 Sensitivity chart of TiO2 with NH3 plasma treatment during 5 minutes
Fig 4.5 I-V curves of TiO2 membrane with NH3 plasma treatment during 10 minutes
Sensitivity_TiO2_NH3 plasma 10mins_PH=1-13
y = 0.038x + 1.7666 R2 = 0.9446
0 0.5 1 1.5 2 2.5
0 2 4 6 8 10 12 14
ph
Vg
Fig 4.6 Sensitivity chart of TiO2 with NH3 plasma treatment during 10 minutes
Fig 4.7 I-V curves of TiO2 membrane with NH3 plasma treatment during 20 minutes
Sensitivity_TiO2_NH3 plasma 20mins_PH=1-13
y = 0.0311x + 2.5382 R2 = 0.9691
2.5 2.55 2.6 2.65 2.7 2.75 2.8 2.85 2.9 2.95 3
0 2 4 6 8 10 12 14
ph
Vg
Fig 4.8 Sensitivity chart of TiO2 with NH3 plasma treatment during 20 minutes
Fig 4.9 I-V curves of TiO2 membrane with NH3 plasma treatment during 30 minutes
Sensitivity_TiO2_NH3 plasma 30mins_PH=1-13
y = 0.0241x + 1.7998 R2 = 0.9234
1.75 1.8 1.85 1.9 1.95 2 2.05 2.1 2.15
0 2 4 6 8 10 12 14
ph
Vg
Fig 4.10 Sensitivity chart of TiO2 with NH3 plasma treatment during 30 minutes
Fig 4.11 I-V curves of TiO2 membrane with NH3 plasma treatment during 60 minutes
Sensitivity_TiO2_NH3 plasma 60mins_PH=1-13
y = 0.0304x + 1.3475 R2 = 0.9868
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
0 2 4 6 8 10 12 14
ph
Vg
Fig 4.12 Sensitivity chart of TiO2 with NH3 plasma treatment during 60 minutes
TiO2
0 10 20 30 40 50 60
S en sitiv ity
w/o plasma treatment 55.8 55.8 55.8 55.8 55.8
with plasma treatment" 51.7 37.5 32.5 22.5 30
5mins 10mins 20mins 30mins 60mins
Fig 4.13 The tendency of various plasma treating time interval of TiO2
Fig 4.14 I-V curves of ZrO2 without plasma treatment
Sensitivity_ZrO2_PH=1-13
y = 0.063x + 2.1959 R2 = 0.9993
0 0.5 1 1.5 2 2.5 3 3.5
0 2 4 6 8 10 12 14
ph
vg
Fig 4.15 Sensitivity chart of ZrO2 without plasma treatment
Fig 4.16 I-V curves of ZrO2 membrane with NH3 plasma treatment during 5 minutes
Sensitivity_ZrO2_NH3 plasma 5mins_PH=1-13
y = 0.0589x + 2.0361 R2 = 0.9955
0 0.5 1 1.5 2 2.5 3
0 2 4 6 8 10 12 14
ph
Vg
Fig 4.17 Sensitivity chart of ZrO2 with NH3 plasma treatment during 5 minutes
Fig 4.18 I-V curves of ZrO2 membrane with NH3 plasma treatment during 10 minutes
Sensitivity_ZrO2_NH3 plasma 10mins_PH=1-13
y = 0.0475x + 1.6118 R2 = 0.9834
0 0.5 1 1.5 2 2.5
0 2 4 6 8 10 12 14
ph
Vg
Fig 4.19 Sensitivity chart of ZrO2 with NH3 plasma treatment during 10 minutes
Fig 4.20 I-V curves of ZrO2 membrane with NH3 plasma treatment during 20 minutes
Sensitivity_ZrO2_NH3 plasma 20mins_PH=1-13
y = 0.0482x + 2.6796 R2 = 0.9879
0 0.5 1 1.5 2 2.5 3 3.5
0 2 4 6 8 10 12 14
ph
Vg
Fig 4.21 Sensitivity chart of ZrO2 with NH3 plasma treatment during 20 minutes
Fig 4.22 I-V curves of ZrO2 membrane with NH3 plasma treatment during 30 minutes
Sensitivity_ZrO2_NH3 plasma 30mins_PH=1-13
y = 0.0393x + 1.4136 R2 = 0.9641
0 0.5 1 1.5 2 2.5
0 2 4 6 8 10 12 14
ph
Vg
Fig 4.23 Sensitivity chart of ZrO2 with NH3 plasma treatment during 30 minutes
Fig 4.24 I-V curves of ZrO2 membrane with NH3 plasma treatment during 60 minutes
Sensitivity_ZrO2_NH3 plasma 5mins_PH=1-13
Fig 4.25 Sensitivity chart of ZrO2 with NH3 plasma treatment during 60 minutes
ZrO2
w/o plasma treatment 62.5 62.5 62.5 62.5 62.5
with plasma treatment 58.3 46.7 47.5 38.3 28.3 5mins 10mins 20mins 30mins 60mins
Fig 4.26 The tendency of various plasma treating time intervals of ZrO2
ZrO2
treated
ZrO2 TiO2
treated
TiO2
Fig 4.27 The coplanar structure