Vacuum and Thin Film Technology
Introduction
The word vacuum is derived from the Greek word meaning empty. In practice, some type of vessel opened to the surrounding air is used. As air is removed by some pumping means, a vacuum is obtained.
Vacuum Lab. has recently expanded into four divisions, and each division is related to specific industrial needs. The four divisions:
- Thin film deposition
- Thin film measurement
- Vacuum pressure and gas flow rate calibration
- Nanotecnology R & D
Thin film deposition
Optical Thin Film
The system is the largest among our coaters. This largest-volume system not only allows cost-effective evaporation process to be performed, it also allows the coating of very large substrate with specialized types of layers, such as remote sensing payload system.
IAD (Ion beam assisted deposition), a well-known technology, is possible to improve the properties of thin film in terms of durability and stability.
The advantages of our vacuum deposition system are as follow:
- Fully automatic operation under microprocessor control
- EB evaporator, specially developed for optical multiplayer coating
- Advanced plasma source available
- Combination of photometer and quartz-crystal measurement for film thickness monitoring
- Advanced pumping system
The future target of this division is to fabricate high resolution electro-optical image module and develop new thin film process.
Thin film measurement
The properties of thin film measurement division include optical reflective index, transmittance, reflectance, spectrum analysis, hardness, adhesion and thickness. The thin film thickness and structure is determined by x-ray diffraction and surface topography.
Vacuum pressure and gas flow rate calibration
Vacuum pressure calibration
The Vacuum Instrument Group was established in 1977 in recognition of its importance with respect to the manufacturing and maintenance of instruments. This group has the capability to design and manufacture items ranging from basic components to complete vacuum systems. At the present time, PIDC is ready to apply for accredititation for the vacuum standard from our National Bureau of Standards.
Vacuum pressure calibrations:
- Vacuum gauge calibration for the range of 1 atm – 10−7 Torr
- Leak detection vacuum systems
Orifice-flow system
The orifice-flow system is the commonest system used in the calibration and measurement of high vacuum. For an infinite thin aperture in the molecular flow regime, the conductance is a constant and directly related to the rate of impingement of molecules over the aperture. The pressure in the upper and lower chambers thus can be determined if the flow rate and the pumping speed of the foreline pump are given. However the actual pressure distribution inside the chamber restricts the accuracy of the calibration or measurement.
The flow field inside a cylindrical vacuum chamber of an orifice-flow systemis investigated using the direct simulation Monte Carlo (DSMC) method. A known gas flow is introduced to the upper chamber through a port in the center of the top plate and the outlet boundary is set to be a known pressure to represent a specific foreline pump. The upper chamber contains no molecules at the beginning of the simulation. The number of the molecules in the chamber raises up after the molecules come in from the inlet port and finally achieves a steady state. The observation is focused on the pressure distribution in the chamber, especially at the position where the vacuum gauges locate and the area around the baffles.
Orifice-flow system
Nanotechnology R & D
Chemical Beam Epitaxy (CBE)
III-V compound semiconductors including (In, Ga, Al)N elements have attracted a significant interest as an active layer in optoelectronic devices. High brightness blue and green light emitting diodes (LEDs) and blue laser diodes (LDs) have been fabricated using GaN/InGaN heterostructures epitaxial layers as active layers. Among the various growth techniques used for the in-situ preparation of GaN epitaxial layers, such as MOCVD has become increasingly important. MBE, however, is superior to MOCVD with respect to composition, thin film quality and thickness control, allowing monolayer resolution through in-situ monitoring (RHEED) and shutter control. On the other hand, problems such as lower scale-up, however, limit the use of MBE systems. In order to overcome these problems MOMBE has been developed which is one of the most promising techniques for fabricating future electronic devices.
Chemical Beam Epitaxy System
Growth of GaN epitaxial layers and InGaN/GaN heterostructures on sapphire substrates by chemical beam epitaxy (CBE)/metalorganic molecular beam epitaxy (MOMBE) and the corresponding microstructure-optoelectronic characterization were studied using triethyl gallium (TEGa) and rf-plasma excited active nitrogen. The system which combines the advantages of both metalorganic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE).
In this project, GaN epitaxial layers were grown by using build CBE which combine several advantages such as ultra high vacuum degree, high operation temperature, MO source materials and radio frequency (rf) excited nitrogen. Growth factors of GaN were controlled. The operation temperature, pressure, flow rate of nitrogen gas (N2) and rf power were controlled in all experiments. The intensity of optical emission from nitrogen plasma, originating from excited atomic nitrogen (N*), was monitored and used as the N* supply rate. The grown layers were characterized by in-situ RHEED, Photoluminescence Spectrometer (PL), X-ray diffraction (XRD) , Energy Dispersive Spectrometer (EDS), Scanning Electron Microscope (SEM) and field-emission transmission electron microscope (FE-TEM).
Pulse Laser Deposition (PLD)
In recent years, the ferroelectric materials have been widely deployed in optical and semiconductor products because of their special dielectric and piezoelectric properties. In particular, complex perovskite materials have shown potential application due to their extremely high permittivity and piezoelectric coefficient. We will investigate the PZN-xPT and PMN-xPT epitaxial thin films grown by pulsed laser deposition (PLD) for different x and various lattice plane orientations. Using x-ray reflectivity, AFM and SEM will help us to control the qualities of the thin films and get the best growth condition respectively, i.e. thickness and roughness etc.
Pulse Laser Deposition System
Dielectric permittivities, piezoelectric parameter, refraction index, polarization-electric field hysteresis loops, dc conductivity and polarizing microscope will be measured to further realize the physical features of ferroelectric materials. To fabricate ferroelectric thin film is more useful for the application of the micromechanic system and micro-optical industry.
