3-1 ZrZnO Film Analisys
3-1-1 The FTIR Measurement of ZrZnO Films
The principle of FTIR is that the energy of the molecules of our samples in unoccupied excited rotational and vibrational states , which is different from the ground-states , can correspond to photon energies found in the infrared. These can be detected and identified by FTIR. Figure1-2 shows the corresponding peaks of FTIR for Zr0.03Zn0.97O thin films . There are three peaks in the wavelength (cm-1) of 437 , 617 and 675. These peaks belonged to ZnO. There is one peak in the wavelength (cm-1) of 3500. These peaks belonged to O-H bonding . Figure3-1 shows the corresponding peaks of FTIR for ZrO. There are five peaks in the wavelength (cm-1) of 474, 530, 575, 630, 645. These peaks belonged to ZrO2. The Zr-O bonding is not found in Zr0.03Zn0.97O thin films by the FTIR measurement.
Figure3-2 illustrates the FTIR measurement result of varied baking temperature Zr0.03Zn0.97O film on a single crystalline Silicon substrate. In this studies , we find out that the organic bonding can be removed completely by baking procedures.
Figure3-3 illustrates the FTIR measurement result of 350°C curing temperature
Zr0.03Zn0.97O film on a single crystalline Silicon substrate at varied baking temperature.
In this studies , we find out that the organic bonding can be removed completely at 350°C.
In other words , no organic peaks were detected in the Zr0.03Zn0.97O thin films by FTIR where the curing temperature is higher than 350°C.
3-1-2 The SEM Measurement of ZrZnO Films
The Scanning Electron Microscope 〈SEM〉 is a microscope that uses electrons rather than light to form an image. There are many advantages to using the SEM instead of a light microscope.
The SEM has a large depth of field , which allows a large amount of the sample to be in focus at one time. The SEM also produces images of high resolution , which means that closely spaced features can be examined at a high magnification.
Preparation of the samples is relatively easy since most SEMs on require the sample to be conductive. The combination of higher magnification , larger depth of focus , greater resolution , and ease of sample observation makes the SEM one of the most heavily used instruments in research areas today.
We can check the grain size of ZnO and Zr0.03Zn0.97O thin films by SEM measurement . Figure3-4 illustrates the SEM measurement result of the ZnO thin films curing at 350°C under oxygen environment. Figure3-5 illustrates the SEM measurement result of the Zr0.03Zn0.97O thin films curing at 350°C under oxygen environment. , Before, we used SEM to analysis the ZnO and Zr0.03Zn0.97O films.
Now , We want to find out the grain size of Zr0.03Zn0.97O thin films with different spin-coating times by SEM measurement. In our studies, we use SEM to analysis the Zr0.03Zn0.97O films which are 400~500A and 1100~1200A. Figure3-6 illustrates the SEM measurement result of the Zr0.03Zn0.97O thin films coating with active layer thicknesses ranging from 400A to 500A. Figure3-7 illustrates the SEM measurement result of the Zr0.03Zn0.97O thin films coating with active layer thicknesses ranging from 1100A to 1200A.
From the analysis by SEM, we can conclude that Zr0.03Zn0.97O thin film contained an amorphous incubation layer at the substrate interface and increased grain at the top of the film. As thickness of the thin film increases its grain size also increases , the complicated structure of Zr0.03Zn0.97O thin films can be schematized as shown in Figure3-8
3-1-3 The AFM Measurement of ZrZnO Films
In my studies, I use Atomic Force Microscopy〈AFM〉to analysis the roughness of the Zr0.03Zn0.97O thin film. The atomic force microscope 〈 AFM 〉 is a very high-resolution type of scanning probe microscope, with demonstrated resolution of fractions of an Angstrom, more than 1000 times better than the optical diffraction limit.
The AFM was invented by Binnig,Quate and Gerber in 1986, and is one of the foremost tools for imaging, measuring and manipulating matter at the nanoscale.
Figure3-9 illustrates the AFM measurement result of the Zr0.03Zn0.97O thin films baking at 250°C under oxygen environment. Figure3-10 illustrates the AFM measurement result of the Zr0.03Zn0.97O thin films baking at 300°C under oxygen environment. Figure3-11 illustrates the AFM measurement result of the Zr0.03Zn0.97O thin films baking at 350°C under oxygen environment.
From the analysis by AFM , we can conclude that the uniformity decrease with higher temperature. The best roughness is baking at 250°C. But we can not remove organic bond at 250°C , so we use two-step baking to solve this problem. First , we put the Zr0.03Zn0.97O -TFTs on the hotplate at low temperature to get an uniform thin films and then we put the Zr0.03Zn0.97O -TFTs in the Furnace at 350 °C to remove organic bonding.
Figure3-12 illustrates the AFM measurement result of the Interface contact layer
with SiNx dielectric . Figure3-13 illustrates the AFM measurement result of the Interface contact layer with HfOx / SiNx dielectric.
From the analysis by AFM , we can conclude that the uniformity of HfOx / SiNx dielectric layer is the best. On the other hand , it can improve effectively roughness of the interface between the semiconducting layer and the gate insulator.
3-1-4 The XRD Measurement of ZrZnO Films
X-ray Diffraction 〈XRD〉measurement result can indicate that preferred orientation of the Zr0.03Zn0.97O film is c-axis perpendicular to the substrate. X-ray Diffraction〈XRD〉is one of the most important non-destructive tools to analyse all kinds of matter - ranging from fluids , to powders and crystals. From research to production and engineering , XRD is an indispensible method for materials
characterization and quality control. Rigaku has developed a range of diffractometers , in co-operation with academic and industrial users , which provide the most
technically advanced , versatile and cost-effective diffraction solutions available today.
Figure3-14 illustrates the XRD measurement result of varied thickness
Zr0.03Zn0.97O films on a single crystalline Silicon substrate. It can be seen that all of the compositions exhibited (002) peak at 2θ=34.2 degree and belonged to the
hexagonal wurtzite structure of Zr0.03Zn9.97O. And the (100) peak was appeared and it
also belonged to the hexagonal wurtzite structure of Zr0.03Zn0.97O.
In this studies , we find out that the varied thickness can not effect the orientation of the Zr0.03Zn0.97O films by spin-coating times.
3-1-5 The XPS Measurement of ZrZnO Films
The X-ray Photoelectron Spectroscopy〈XPS〉 technique is highly surface specific due to the short range of the photoelectrons that are excited from the solid. The energy of the photoelectrons leaving the sample are determined using a Concentric Hemispherical Analyser and this gives a spectrum with a series of photoelectron peaks. The binding energy of the peaks are characteristic of each element. The peak areas can be used (with appropriate sensitivity factors) to determine the composition of the materials surface. The shape of each peak and the binding energy can be slightly altered by the chemical state of the emitting atom. Hence XPS can provide chemical bonding information as well.
First , we rose the temperature from 350°C to 500°C to analysis the oxygen vacancy (Vo) of the Zr0.03Zn0.97O thin films. We can have different full lines for O 1s from 350°C to 500°C . Then , it get two main peak in banding evergy for three different
figure by fitting . The binding evergy of varied element can be observed for the
Zr0.03Zn0.97O thin films as shown in Table 8. One is Zn-O binding evergy〈530.15 eV〉, another is oxygen vacancies binding evergy〈531.25 eV〉. Figure3-15 illustrates the XPS measurement result of the Zr0.03Zn0.97O thin films curing at 350°C under oxygen environment. Figure3-16 illustrates the XPS measurement result of the Zr0.03Zn0.97O thin films curing at 425°C under oxygen environment. Figure3-17 illustrates the XPS measurement result of the Zr0.03Zn0.97O thin films curing at 500°C under oxygen environment.
In this studies , we find out that an peak at oxygen vacancies (Vo) is observed clearly than Zn-O by the analysis of XPS with higher temperature . In the words , it reveals that oxygen vacancy (Vo) increase for the Zr0.03Zn0.97O thin films with higher temperature.
3-2 The Electrical Characteristics of ZrZnO based TFTs
3-2-1 Baking with various temperature
We put Zr0.03Zn0.97O thin films on hotplate to remove the solvent and organic residuals bonding. The temperatures were 250, 300 and 350°C. Figure3-18 shows the ID-VD of comparison between baking temperature 250~350°C by hot plate. And the annealing temperature is 350°C and pressure is 0.6 torr with W/L=50/3 µm.
From the electrical characteristic , we can conclude that The condition of baking 300°C for 10 min shows a maximum saturated current (Isat). The condition of baking 300°C for 10 min shows the best semiconducting property.
3-2-2 Annealing with various temperature
We put Zr0.03Zn0.97O thin films in Vacuum Annealing Furnace under 0.3 torr oxygen ambient and the temperature are 350 425 500°C. When we annealed Zr0.03Zn0.97O TFTs with 500°C for 1 hr, it shows a normally on phenomenon. This result attribute to bigger grain size and higher carrier concentration. Figure3-19 show the ID-VGof our Zr0.03Zn0.97O based-TFTs devices with the condition of annealed under 0.3 torr oxygen ambient with different temperature 350 425 500°C for 1 hr. Figure3-20 shows the ID-VD of our Zr0.03Zn0.97O based-TFTs devices with the condition of annealed under 0.3 torr oxygen ambient with different temperature 350 425 500°C for 1 hr.
Table 9 shows electronic properties of Zr0.03Zn0.97O based-TFTs with different
baking conditions but at the same 350°C curing temperature . The maximum mobility (µ) of Zr0.03Zn0.97O based-TFTs is 1.5*10-4 V-1.s-1 , where the curing temperature is 425°C. The minimum threshold voltage (Vt) of Zr0.03Zn0.97O based-TFTs is 21.3 volt , where the curing temperature is 425°C. According to the Table 9 , the threshold voltage (Vt) decreased with higher curing temperature.
So , It can be deduced that oxygen vacancy (Vo) increases with higher temperature when the samples were annealed in oxygen atmosphere. For
Zr0.03Zn0.97O thin films , the change in the concentration of the oxygen vacancy(Vo) could lead to the change of the electron concentration. It reveals that oxygen vacancy (Vo) increase with higher curing temperature to have more carrier concentration.
From the electrical characteristic , we can conclude that oxygen vacancy (Vo) and free carrier increase with higher temperature. Therefore , when we annealed at 500°C , the electronic characteristic exhibited normally-on characteristic for Zr0.03Zn0.97O based-TFTs.
3-2-3 Spin-coating with various film thickness
We put Zr0.03Zn0.97O thin films with varied thickness in Vacuum Annealing Furnace at 350°C under oxygen ambient 0.6 torr. Figure 3-21 shows the ID-VG of our devices
with the condition of thicknesses ranging 400~500A , 1100~1200A , 1400~1500A annealed at 350°C under oxygen ambient with for 1 hr. Figure 3-22 shows the ID-VD of our devices with the condition of thicknesses ranging 400~500A , 1100~1200A , 1400~1500A annealed at 350°C under oxygen ambient with for 1 hr.
Table 10 shows the threshold voltage (Vt) , mobility (µ) and on/off current (Ion/off) of the varied thickness. It can be seen that the threshold voltage (Vt) decreased dramatically with thickness of the thin film. The mobility (µ) increased dramatically with thickness of the thin film. The maximum mobility (µ) of Zr0.03Zn0.97O based-TFTs was 6.0X10-4 V-1.s-1 , where the thickness of the thin film is between 1100A ～ 1200A. The minimum threshold voltage (Vt) of Zr0.03Zn0.97O based-TFTs was 18.6 volt , where the thickness of the thin film is between 1100A ～ 1200A. The maximum on/off current (Ion/off) of Zr0.03Zn0.97O based-TFTs was 7.4*105 , where the thickness of the thin film is between 1100A ～ 1200A.
From the electrical characteristic , we can conclude that it is clearly visible that increasing the active layer thickness, leads to higher on-current . off-current and lower Vt.
Concerning the variation of the on-current , It can be deduced that carrier concentration increases with thickness , leading to an higher flow of electrons pass through the channel layer until 1100A ～ 1200A . Concerning the variation of the
off-current , it surely is related that more carrier can not be controlled with increasing thickness for gate electrode , leading to the leakage current is oversized where the thickness of the thin film is between 1400A ～ 1500A. Concerning the decrease of Vt with increasing thickness , The grain size increase with thickness of the thin film.one can possible consider that result a consequence of the higher number of free carrier in the bulk of the thicker semiconductor because of the grain size , thus conducting to an easier accumulation of charges in the semiconductor / dielectric interface than in thinner films . The characteristic of thickness of the Zr0.03Zn0.97O thin films between 1100A ～ 1200A is the most suitable at present.
3-2-4 Interface contact layer with various dielectric
In this chapter , we use two kinds of dielectric layer , SiNx and HfOx / SiNx. Figure 3-23 shows the ID-VG of our devices with the condition of Interface by different
dielectric layer SiNx and HfOx / SiNx . Figure 3-24 shows the ID-VD of our devices with the condition of Interface by different dielectric layer SiNx and HfOx / SiNx .
Table 11 shows the threshold voltage (Vt) , mobility (µ) and saturated current (Isat) of the varied Interface. It can be seen that the threshold voltage (Vt) decreased dramatically with dielectric layer HfOx / SiNx . The mobility (µ) increased dramatically
with dielectric layer HfOx / SiNx . The saturated current (Isat) increased slightly with dielectric layer HfOx / SiNx . The mobility (µ) of Zr0.03Zn0.97O thin film transistor was 9.0X10-5 V-1.s-1 with dielectric layer HfOx / SiNx. The threshold voltage (Vt) of Zr0.03Zn0.97O thin film transistor was 19.5 volt with dielectric layer HfOx / SiNx. The saturated current (Isat) of Zr0.03Zn0.97O thin film transistor was 1.4X10-9 A with dielectric layer HfOx / SiNx.
From the electrical characteristic , we can conclude that with dielectric layer HfOx / SiNx. The very smooth HfOx / SiNx films ensure both high-quality Zr0.03Zn0.97O layers and Zr0.03Zn0.97O / HfOx interfaces, resulting in improved carrier mobility due
potentially to both reduced disorder in the Zr0.03Zn0.97O film as well as reduced interfacial scattering.