| dc.description.abstract | The tendency of developing ultrasonic printing technology is increasing in the commercialized printing devices, which incorporate with ultrasonic ejectors. In this thesis, the influences of fabrication parameters on the characteristics of four-level Fresnel lens and piezoelectric transducers, which are the two main components of an ultrasonic ejector, will be presented and discussed.
The design and fabrication of Fresnel focusing lenses operating at frequencies of 100 and 200 MHz was investigated in order to enhance the focusing efficiency of ultrasonic energy. The effects of process parameters on the four-level Fresnel lens profiles were discussed to find a most feasible fabrication procedure through some trial experiments. A fabrication process employing a two-mask without using a hard mask was first carried out. The profile of four-level Fresnel lens was shaped even it was not really expected. The quality of the Fresnel lens was improved when two- and three-mask processes using a SiO2 film as the hard mask are employed. Besides, a better side-wall profile of Fresnel lens was obtained by using the three-mask process as compared to the two-mask one. In addition, a two-mask fabrication process of a four-level Fresnel lens was used to evaluate its characteristics through investigating the effect of SU-8 photoresist on the profile of the focusing lens. Besides, an investigation of the influence of surface profile on the efficiency was proposed to evaluate the acoustic energy focusing efficiency of the fabricated Fresnel lens. The simulation results of the FEM showed that it can be a useful tool to estimate the efficiency of Fresnel lenses through their surface profiles in trailed fabrications.
For design and fabrication of the piezoelectric transducer, the influences of factors that can affect the crystallization growth of ZnO films were figured out and investigated. The influences of aluminum (Al), platinum (Pt) with/without heat treatment, RF power and the Ar:O2 gas ratio; substrate temperature on the crystallization growth of ZnO films were
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proposed and discussed. Indeed, highly c-axis (002) oriented ZnO films were successfully deposited on Pt (annealed)/Ti/SiO2/Si substrates under feasible conditions, such as RF power of 178 W, substrate temperature of 380 C, deposition pressure of 10mTorr and Ar:O2 gas flow ratio of 50%. Besides, a two-step deposition of ZnO films was proposed to develop a feasible fabrication of a piezoelectric transducer with the structure Al/ZnO/Pt/Ti/SiO2/Si under reasonable conditions, which include deposition pressure of 0.7 Pa and 1.3 Pa, RF power of 100 W and 178 W, and sputtering gas ratio Ar:O2 = 1:3 and 1:1 for first and second step, respectively. These conditions were applied and confirmed through investigating the influences of deposition parameters on the properties of ZnO films. Highly c-axis textured and other reasonable properties of ZnO films were confirmed. | en_US |