Chapter 2 Experiment…
2.4 The process of measurement
1. Before the measurement, the B and P ion was implanted to form the N-type and P-type SiGe nanowire.
2. The measure condition was set VD = −10V to 10V in 0.2V step and VG = −15 V, 0 V and 15 V respectively.
3. The 3-aminopropy-ltriethoxysilane (APTES) was used to modify the surface, which can detect the charge with different pH.
4. Drip pH 1 solution, and then the surface was dried by nitrogen purge.
5. D.I. Water was utilized to wash the surface after measurement.
6. Repeat 4 and 5 by pH 3, 5,9,11.
Chapter 3
Results & Discussion
3.1 SiGe Nanowire Fabrication
We have successfully fabricated the SiGe nanowire structure on the Si wafer by spacer technique and measured the electric characteristics. As we known, the diameter of the nanowire would influence the current, so the control of the nanowire would become a key issue. This was controlled by the Mask #02 when we etched the SiGe film by TCP poly etcher – TCP 9400 SE. The surface of the nanowire is quite sensitive so that it’s easy influence by any variances.
3.2 Cross-Section View of SEM
We observed the cross-section view of different concentration nanowire by Scanning Electron Microscopy (SEM). The area of the nanowire could be calculated by the TFSEM. The JOEL JSM 6500-F – TFSEM was the equipment we used to measure the diameter of the nanowires. Fig. 3-1 shows the cross-section view SEM picture of Si0.93Ge0.07 nanowire. There was fluctuation in each width and height which was controlled by the TCP dry etcher. The fluctuation must be decreased because the diameter of the nanowire is directly related to the current. The average of the Si0.93Ge0.07 nanowire is 192 nm in height and 77.7 nm in width. We thought that the nanowire was a triangle column shape, so the average area is about 14918.4 nm2. Similarly, Fig. 3-2~3-5 show the cross-section view SEM picture of SiGe nanowires with different Ge concentration. All the data are summarized on the Table 1.
3.3 Make the nanowire Comparison of N-type and P-type
Electrical-transport measurements were conducted using an Agilent 4156C semiconductor parametric analyzer. We sweep the ID-VD figure from –10V to 10V, and change the VG step from –15, 0V and 15V. Fig. 3-6 show the ID-VD figure of the Si0.93Ge0.07 nanowire of P-type with the length L=5µm. For comparison, we fabricated the same nanowire of N-type (Fig. 3-10) and the same way to measured. Similarly, we compared the electronic properties of Fig 3-7 to 3-9 and Fig.3-11 to 3-13. It seems that the current of the N-type nanowire would be larger than that of P-type nanowire.
3.4 The same concentration of Ge with different pH solution
Before the measurement, the P and B ions were implanted to form the N–type and P–type SiGe nanowire, respectively. The 3-aminopropy-ltriethoxysilane (APTES) was used to modify the surface, which can detect the charge with different pHs. Fig. 3-14 shows the ID-VD curves of P-type Si0.93Ge0.07 nanowire with pH3, pH5, pH9 and pH11 solutions at VG
= –15V and VD = –10V to 10V. The higher current is obtained for pH11 solution.
Similarly is shown in Fig. 3-15~3-18, current increase with the incensement of pHs under the different concentration of Ge. On the other way, Fig. 3-19 shows the ID-VD curves of N-type Si0.93Ge0.07 nanowire with pH3, pH5, pH9 and pH11 solutions at VG = –15V and VD = –10V to 10V. The higher current is obtained for pH3 solution. Similarly is shown in Fig. 3-20~3-22, current decrease with the incensement of pHs under the different concentration of Ge.
3.5 The comparison of conductance and conductivity with different pH solution
The equation about resistance R is
∆V = ∆I · R = ∆I · ρ (L/A) → (3.1) conductance :(1/R)=( ∆I / ∆V ) → (3.2)
ρ is the resistivity. The (1/R) is the conductance (S).We fix the voltage ∆V at
0.2V to be constant. Using the formula (3.2), conductance of nanowire can be calculated. The average conductance between –4 V to –8 V was obtained. The conductance of P-type Si0.93Ge0.07 nanowire increases as the enhancement of pH solution (Fig. 3-23). Fig. 3-24~3-27 show the conductance versus pH in other Ge concentrations, and all the figures show the enhancement in higher pH solution. Contrasting the P-type nanowire, the trend of conductance with N-type Si0.93Ge0.07 nanowire become lower as increase of pHs solution (Fig. 3-28). Fig.3-29~3-31 show the conductance versus pH in other Ge concentrations, and all the figures show the conductance decrease as the pH increase. All the data were summarized on the table 2.
3.6 The influence of Ge on the sensitivity of the nanowire
As we known, there is still some reason will affect the drive current including the diameter of the nanowire, wire length, the dopant condition, heat treatment, and the electrode contact, etc. According to the above reasons, we should normalize the current by conductance or conductivity if we want to compare the five structures. Rewrite the (3.1) equation, the σ is
ρ= A · (∆V / ∆I) / L
σ = L / [ A · (∆V / ∆I) ] → (3.3)
σ is the conductivity (S/m). L is the device length. A is the area of the nanowire. Using the formula (3.3) and the area, conductivity of nanowire can be calculated. In order to decrease the error in measurement, the average conductivity between -4V to -8V was obtained.
Percentage of conductivity increase (%) = (pH9-pH5)/pH5 → (3.4)
The formula (3.4) is used to calculate the change in conductivity with the same pH change (Fig. 3-32). The pH9 is the conductivity for pH=9 and the pH5 is the conductivity for pH=5. The percentage change of conductivity is 3.9% in P-type Si0.93Ge0.07 nanowire, 6.6% in P-type Si0.89Ge0.11 nanowire, 22.6% in P-type Si0.80Ge0.20 nanowire, 38.2% in P-type Si0.70Ge0.30 nanowire and 10.5% in P-type Si0.60Ge0.40 nanowire. Fig. 3-34 shows the percentage change of P-type nanowire between pH5 and pH11 similarly. The percentage change is 4.6% in Si0.93Ge0.07 nanowire, 8.4% in Si0.89Ge0.11 nanowire, 34.2% in Si0.80Ge0.20 nanowire, 47.9% in Si0.70Ge0.30 nanowire and 49.6% in Si0.60Ge0.40 nanowire.
It is observed that the sensitivity improves with the increment of Ge concentration from 7% to 30%. The sensitivity doesn’t increase at the higher concentration of Ge (40%) in pH5 VS. pH9 but enhances in pH5 VS. pH11. The reason for reduces of the sensitivity at 40%-Ge concentration may be higher defects appears at the interface. It may cause the bad adhesion between APTES and the surface of SiGe nanowire, which result in the nonlinear conductance change within different pH solution.
On the other hand, the percentage change of conductivity is -2.5% in n-type
Si0.93Ge0.07 nanowire (Fig. 3-33), -4.27% in n-type Si0.89Ge0.11 nanowire, -4.44%
in n-type Si0.80Ge0.20 nanowire and -10.6% in n-type Si0.70Ge0.30 nanowire. Fig.
3-35 shows the percentage change of n-type nanowire between pH5 and pH11 similarly. The percentage change is -3.1% in Si0.93Ge0.07 nanowire, -5.94% in Si0.89Ge0.11 nanowire, -10.5% in Si0.80Ge0.20 nanowire and -17.2% in Si0.70Ge0.30 nanowire.
Although the n-type of SiGe nanowire(40%) was failure. But it is clearly observed that the sensitivity improves with the enhancement of Ge concentration from 7% to 30%.
Chapter 4 Conclusion
In this thesis, we have successfully fabricated the SiGe nanowire with different Ge concentration by spacer technique on silicon wafer. P and B implant is used to form the N-type and P-type SiGe nanowire. The electrical properties were measured by HP 4156C and the structure of the SiGe nanowire on the sidewall spacer was observed by SEM.
The sensitivity is the most important key issue for the nanowire as a sensor.
The major mechanism of nanosensor is measuring the change of current as the material adsorbed on the surface. The 3-aminopropy- ltriethoxysilane (APTES) was used to modify the surface, which can detect the charge with different pH solution. The conductance and conductivity is used to quantify the change with different pH solution. The percentage change of conductivity among pH5, pH9 and pH11 is calculated to confirm the improvement of SiGe nanowire with different Ge concentration. It is clearly observed that the sensitivity is improved by using higher Ge concentration nanowire instead of lower Ge concentration nanowire (7%~30%) in both N-type nanowire and P-type nanowire. But our experiment found the higher Ge concentration (40%) has not increased the sensitivity; the reason maybe the higher defect appears at the surface as over-high Ge concentration.
Chapter 5 Future Work
In future, we will oxidize the nanowire. The nanowire surface oxidizes treatment utilizes N2O or a small amount of oxygen, improve the electric characteristic which nanowire. The Ge segregation would happen when the SiGe film by oxidized. This could lead to higher Ge concentration in the SiGe film.
Increase the Ge concentration by oxidation may be a feasible way. We can improve the proportion in the silicon germanium alloy of germanium and mend the defect easily, and then cause the higher sensitivity.
Current Current Preamplifier
Preamplifier LockLock-in Amplifier-in Amplifier Current
Preamplifier LockLock-in Amplifier-in Amplifier Current
Preamplifier LockLock-in Amplifier-in Amplifier Current
Preamplifier LockLock-in Amplifier-in Amplifier Current
Fig. 1-1 Schema of Scanning Probe Lithography (SPL).
Fig. 1-2 Schematic process flow of nanoimprint (a) After nanoimprint and removal of residual PMMA by O2 plasma (b) Pt evaporation and lift-off.
(a)
(b)
Fig. 1-3 (a) Binary Phase Diagram for the Au:Ge. (b) An SEM image of Ge nanowires synthesized by CVD at 275℃ on a SiO2/Si substrate. The inset shows an AFM image of Au nanoclusters on the substrate recorded prior to CVD.
Fig. 1-4 Schematic view of iterative spacer lithography (ISL).
.
Fig. 1-5 The mechanisms of the laser ablation formation technique.
Fig. 1-6 (a) VLS mechanism : the flux droplet is a metal such as Au, Ag, Pd, Pt, Ni, or Cu are elements of the crystal phase dissolved in the metallic flux droplet. (b) SLS mechanism : the flux droplet is In, and M and E are elements of the III-V semiconductor dissolved in the flux droplet.
Fig. 1-7 Fabrication of a polyaniline nanowire immobilized on a Si surface with stretched double-stranded DNA as a guiding template.
Fig. 1-8 Conductance responses of the polyaniline nanowire arrays to vapors of (a) HCl and (b) HCl followed by NH3.
Fig. 1-9 (A) electrochemically grown single Pd nanowire with 100 nm diameter, (B) hydrogen sensing circuit diagram using single Pd nanowire (100 nm), and (C) 0.1%, 1.0%, 5.0 and 10% hydrogen concentration as a function of output voltage variation and time to confirm reproducibility.
Fig. 1-10 (a) ZnO nanowire sensing response to different concentrations of NO2 . (b) Nanowire sensing response to 1% NH3 at 300 K, and the negative gate field induces a surface refresh process.
Fig. 1-11 ZnO nanowire reducing sensing to NH3 at 500 K.
Fig. 1-12 The response of nanowire conductance to 0.5% CO in 20% O2 at 500 K.
The drain–source voltage here is 0.5 V.
Fig. 1-13 NW nanosensor for pH detection. (A) Schematic illustrating the conversion of a NWFET into NW nanosensors for pH sensing. The NW is contacted with two electrodes, a source (S) and drain (D), for measuring conductance. Zoom of the APTES-modified SiNW surface illustrating changes in the surface charge state with pH. (B) Real-time detection of the conductance for an APTESmodified SiNW for pHs from 2 to 9; the pH values are indicated on the conductance plot. (inset,top) Plot of the time-dependent conductance of a SiNW FET as a function of the back-gate voltage.(inset, bottom) Field-emission scanning electron microscopy image of a typical SiNW device. (C)Plot of the conductance versus pH; the red points (error bars equal ± 1 SD) are experimental data,and the dashed green line is linear fit through this data. (D) The conductance of unmodified SiNW(red) versus pH. The dashed green curve is a plot of the surface charge density for silica as afunction of pH.
Fig. 1-14 Real-time detection of protein binding. (A) Schematic illustrating a biotin-modified SiNW (left) and subsequent binding of streptavidin to the SiNW surface (right). The SiNW and streptavidin are drawn approximately to scale. (B) Plot of conductance versus time for a biotin-modified SiNW, where region 1 corresponds to buffer solution,region 2 corresponds to the addition of 250 nM streptavidin, and region 3 corresponds to pure buffer solution. (C)Conductance versus time for an unmodified SiNW; regions 1 and 2 are the same as in (B). (D) Conductance versus time for a biotin-modified SiNW, where region 1 corresponds to buffer solution and region 2
to the addition of a 250 nM streptavidin solution that was preincubated with 4 equivalents d-biotin.(E) Conductance versus time for a biotin-modified SiNW, where region 1 corresponds to buffer solution, region 2 corresponds to the addition of 25 pM streptavidin, and region 3 corresponds to pure buffer solution. Arrows mark the points when solutions were changed.
Fig. 1-15 Real-time detection of reversible protein binding. (A) Plot of conductance versus time for a biotin-modified SiNW, where region 1 corresponds to buffer solution, region 2 corresponds to the addition of ~3 µM m-antibiotin (460 µg/ml), and region 3 corresponds to flow of pure buffer solution. (B) Conductance versus time for an unmodified SiNW; regions 1 and 2 are the same as in (A). (C) Conductance versus time for a biotin-modified SiNW, where region 1 corresponds to buffer solution, region 2 corresponds to the addition of bovine IgG (200 µg/ml), and region 3 corresponds to addition of ~3 µM m-antibiotin (460 µg/ml). Arrows mark the points when the solutions were changed.(D) Plot of the conductance change of a biotinmodified SiNW versus m-antibiotin concentration;the dashed line is a linear fit to the four low concentration data points. Error bars equal ± 1SD.
Fig. 1-16 Real-time detection of Ca2+ ions. (A)Plot of conductance versus time for a calmodulin-terminated SiNW, where region 1 corresponds to buffer solution, region 2 corresponds to the addition of 25 µM Ca2+ solution, and region 3 corresponds to pure buffer solution.(B) Conductance versus time for an unmodified SiNW; regions 1 and 2 are the same as in (A).Arrows mark the points when solutions were changed. Calmodulin-modified NWs were prepared by placing a drop (~20 µl) of calmodulin solution (250 µg/ml) on SiNW for 1 hour and then rinsing with water for three times.
Fig. 1-17 Real-time detection of DNA. (a) Conductance of a p-type SiNW modified with DNA probes (CCT AAT AAC AAT) versus time, where the arrow indicates the addition of 25 pM noncomplementary DNA (GGA TCA TTG TTA) solution. (b) Conductance of the same p-type SiNW shown in (a), where the arrow indicates the addition of 25 pM complementary DNA (GGA TTA TTG TTA)solution. (c) Conductance of an n-type SiNW modified with the same DNA probes as in (a) and (b), where the arrow indicates the addition of the 25 pM complementary DNA solution.
5000Å
Fig. 2-1 The thickness of the oxide is 5000Å.
Etch Oxide Step
SiO2
Si-Substrate
2000Å
Fig. 2-2 Mask #01 dry etching 3000 Å from oxide Step.
Fig. 2-3 Before we deposited the SiGe film, we deposited amorphous Si film first. This purpose is due to SiGe and SiO2 has a bad adhesion. The thickness of the amorphous Si film is about 150Å.
(a) (b)
Fig. 2-4 The SiGe film is deposited with the ultra-high-vaccum chemical vapor deposition.
The SiGe film is about 800 Å. (a) The side view, (b) The cross-section view.
(a) (b)
Fig. 2-5 After defining the SiGe pattern by the Mask #02, then etching the whole SiGe up by TCP poly etcher. (a) The schematic shows the top view.(b) The schematics shows the side view, after etching the SiGe film.
Remove one side
(a)
(b) (c)
Fig. 2-6 Remove one side of the parallel SiGe spacer. The schematics of the Mask #03. (a) Top view, (b) Side view, (c) The cross-section view.
Fig. 2-7 After thermal coating Al for 5000 Å.
Fig. 2-8 Defined the Al contact pad in the Mask #04. And then sintering at T=420℃ for 25 min.
Fig. 2-9 The schematics of the two SiGe block film. There is no connection between the two block. This was used to make sure that the SiGe and Al film was etched completely in the isolation area.
Fig. 2-10 The test structure of each block was used to calculate the Al/SiGe contact resistance.
Fig. 3-1 The Cross-Section view of the SEM of Si0.93Ge0.07 nanowire, the Si0.93Ge0.07 nanowire is 77.7 nm in width and 192 nm in height.
Fig. 3-2 The Cross-Section view of the SEM of Si0.89Ge0.11 nanowire, the Si0.89Ge0.11 nanowire is 45.4 nm in width and 184 nm in height.
Fig. 3-3 The Cross-Section view of the SEM of Si0.8Ge0.2 nanowire,the Si0.8Ge0.2 nanowire is 65.9 nm in width and 159 nm in height.
Fig. 3-4 The Cross-Section view of the SEM of Si0.7Ge0.3 nanowire,the Si0.7Ge0.3 nanowire is 54.5 nm in width and 153 nm in height.
Fig. 3-5 The Cross-Section view of the SEM of Si0.6Ge0.4 nanowire,the Si0.6Ge0.4 nanowire is 53.4 nm in width and 172 nm in height.
height width area
Ge07 1.92E-07 7.77E-08 1.49E-14 Ge11 1.84E-07 4.54E-08 8.35E-15 Ge20 1.59E-07 6.59E-08 1.05E-14 Ge30 1.53E-07 5.45E-08 8.34E-15 Ge40 1.72E-07 5.34E-08 9.18E-15
Table 1
VG= -15V
Fig. 3-6 The ID-VD of the P-type Si0.93Ge0.07 nanowire of P-type with the length L=5μm.
VG= -15V
Fig. 3-7 The ID-VD of the P-type Si0.89Ge0.11 nanowire of P-type with the length L=8μm.
VG= -15V
Fig. 3-8 The ID-VD of the P-type Si0.8Ge0.2 nanowire of P-type with the length L=9 μm.
VG= -15V
Fig. 3-9 The ID-VD of the P-type Si0.7Ge0.3 nanowire of P-type with the length L=6 μm.
VG= -15V
Fig. 3-10 The ID-VD of the N-type Si0.93Ge0.07 nanowire of N-type with the length L=5μm.
VG= -15V
Fig. 3-11 The ID-VD of the N-type Si0.89Ge0.11 nanowire of N-type with the length L=8μm.
VG= -15V
Fig. 3-12 The ID-VD of the N-type Si0.8Ge0.2 nanowire of N-type with the length L=9μm.
VG= -15V
Fig. 3-13 The ID-VD of the N-type Si0.7Ge0.3 nanowire of N-type with the length L=6μm.
VG= -15V
Fig. 3-14 The ID-VD of the P-type Si0.93Ge0.07 nanowire of P-type with the length L=19μm.
VG= -15V
Fig. 3-15 The ID-VD of the P-type Si0.89Ge0.11 nanowire of P-type with the length L=5μm.
VG= -15V
Fig. 3-16 The ID-VD of the P-type Si0.8Ge0.2 nanowire of P-type with the length L=10μm.
VG= -15V
Fig. 3-17 The ID-VD of the P-type Si0.7Ge0.3 nanowire of P-type with the length L=6 μm.
VG= -15V
Fig. 3-18 The ID-VD of the P-type Si0.6Ge0.4 nanowire of P-type with the length L=7 μm.
VG= -15V
Fig. 3-19 The ID-VD of the N-type Si0.93Ge0.07 nanowire with the length L=11μm.
VG= -15V
Fig. 3-20 The ID-VD of the N-type Si0.89Ge0.11 nanowire with the length L= 6μm
VG= -15V
Fig. 3-21 The ID-VD of the N-type Si0.8Ge0.2 nanowire with the length L= 50μm.
VG= -15V
Fig. 3-22 The ID-VD of the N-type Si0.7Ge0.3 nanowire with the length L= 15μm.
VG= -15V
Fig. 3-23 The P-type conductance of the Si0.93Ge0.07 nanowire changes with the various pH solution.
VG= -15V
Fig. 3-24 The P-type conductance of the Si0.89Ge0.11 nanowire changes with the various pH solution.
VG= -15V
Fig. 3-25 The P-type conductance of the Si0.8Ge0.2 nanowire changes with the various pH solution.
VG= -15V
Fig. 3-26 The P-type conductance of the Si0.7Ge0.3 nanowire changes with the various pH solution.
VG= -15V
Fig. 3-27 The P-type conductance of the Si0.6Ge0.4 nanowire changes with the various pH solution.
VG= -15V
Fig. 3-28 The N-type conductance of the Si0.93Ge0.07 nanowire changes with the various pH solution.
VG= -15V
Fig. 3-29 The N-type conductance of the Si0.89Ge0.11 nanowire changes with the various pH solution.
Fig. 3-30 The N-type conductance of the Si0.8Ge0.2 nanowire changes with the various pH solution.
VG= -15V
Fig. 3-31 The N-type conductance of the Si0.7Ge0.3 nanowire changes with the various pH solution.
單位 ( S) pH=3 pH=5 pH=9 pH=11 P-type Conductance of Ge 7% 6.05E-06 6.24E-06 6.52E-06 6.83E-06 P-type Conductance of Ge 11% 9.76E-06 1.02E-05 1.09E-05 1.14E-05 P-type Conductance of Ge 20% 4.31E-06 4.52E-06 5.55E-06 6.07E-06 P-type Conductance of Ge 30% 2.40E-06 2.93E-06 4.05E-06 4.33E-06 P-type Conductance of Ge 40% 1.19E-06 1.30E-06 1.44E-06 1.95E-06
單位 ( S) pH=3 pH=5 pH=9 pH=11
N-type Conductance of Ge 7% 8.90E-06 8.50E-06 8.29E-06 8.24E-06 N-type Conductance of Ge 11% 1.69E-05 1.64E-05 1.63E-05 1.60E-05 N-type Conductance of Ge 20% 1.65E-06 1.64E-06 1.57E-06 1.47E-06 N-type Conductance of Ge 30% 2.20E-06 2.08E-06 1.86E-06 1.72E-06 N-type Conductance of Ge 40% Failure Failure Failure Failure
Table 2
VG= -15V
Fig. 3-32 The P-type sensitivity is improves with the increase concentration of Ge at low concentration of Ge. [percentage % = (pH9-pH5)/pH5]
VG= -15V
Fig. 3-33 The N-type sensitivity is improves with the increase concentration of Ge.
[percentage % = (pH9-pH5)/pH5]
VG= -15V
Fig. 3-34 The P-type sensitivity is improves with the increase concentration of Ge.
[percentage % = (pH11-pH5)/pH5]
VG= -15V
Fig. 3-35 The N-type sensitivity is improves with the increase concentration of Ge.
[percentage % = (pH11-pH5)/pH5]
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