Compared to other metals, monocrystal silicon carbide has a number of advantages. It has the highest density and conductivity, it can be molded and machined, it is highly resistant to corrosion, and it is suitable for use in applications that require very high temperature and pressure. The material is used in the manufacturing of disk gyroscopes, acoustic resonators, and a variety of other products.
Among the various semiconductor substrates available, the monocrystalline silicon carbide is by far the most common. This type of silicon is a monocrystalline crystal that has no grain boundaries. Its chemical properties make it a promising material for RF electronics applications, as well as power electronics.
Silicon carbide is typically produced in the following way:
The first step is to form an ingot out of a silicon powder. Then, the powder is reacted with a carbon powder. The mixture is heated in a crucible at a high temperature to produce the SiC compound. This process requires precise control to ensure that the final product meets internal specifications.
The next major process is the growth of the silicon carbide crystal. It is important to note that this process is called 'growth' by the experts, but is actually a process called'sublimation'.
Using gas assisted PVT (GAPVT), monocrystal SiC single crystals can be doped with vanadium in a precise and controlled manner. It has been shown that vanadium doping enhances the electrical resistivity of SiC single crystals, thereby allowing for stable semi-insulating properties. However, high vanadium doping can lower the hardness value of silicon carbide. This study aims to characterize the vanadium concentration in monocrystal SiC single crystals and the associated vanadium doping mechanism.
The first step in doping growing a SiC single crystal with vanadium is introducing the vanadium dopant into the growth environment of the crystal. It is necessary to control the partial pressure of vanadium inside the growth crucible to achieve spatially uniform doping of vanadium. This is achieved by inserting an inert capsule beneath the SiC source. The capsule generally consists of graphite and a calibrated capillary to allow a controlled effusion of vanadium vapor.
During the manufacture of silicon carbide devices, several intrinsic impurities are introduced. These impurities can be classified into three types. Those are: shallow energy level impurities, intrinsic point defects and deep energy level dopants. The difference between shallow energy level impurities and shallow energy level dopants should be less than 5x1017cm-3.
Deep energy level dopants are used to compensate for the shallow energy level impurities. Deep energy level dopants are introduced to maintain the semi-insulating characteristic of SiC. Some of the intrinsic impurities can also be used as the deep energy level dopants. This can be useful for avoiding excessive concentration.
The intrinsic point defects contribute to the quality of the crystal and provide good crystallization characteristics. The depth profiling of the monocrystalline silicon surface shows that the peak concentrations of the impurities elements are very low at the surface. Moreover, the impurities peak concentrations decrease as the detecting depth increases.
Various types of bulk acoustic wave resonators are available in the market. They are monocrystalline or polycrystalline type. They have different area and Kt values. Compared to polycrystalline acoustic wave resonator, monocrystalline resonators have smaller areas. However, they have higher Q values.
One of the first series of resonators is the single crystal acoustic wave resonator. The structure of the resonator is shown in figure 3 and consists of two layers. The first layer comprises resonant layer 22 and electrodes 24 and 26. The lower electrode determines the resonance frequency and the top electrode defines the antiresonance frequency.
The second structure comprises mass loading layer 202 and electrodes 142 and 141. The upper electrode is made of metal and the lower electrode is a dielectric material. The thickness of the first mass loading layer 201 can be adjusted. Besides, the thickness of the second mass loading layer can also be adjusted to improve the performance of the resonator.
Optically-interrogated 100 m thick SiC disks have been designed and fabricated. These disks support nearly degenerate frequency splits between m = 9 elliptical modes at 5.3 MHz. As-fabricated frequency splits are as low as three ppm. They are supported by n-doped monocrystalline on-axis 4H-SiC substrates. This structural design is capable of supporting arrays of ultra-high Q SiC resonators.
During optical interrogation, the m = 3 elliptical mode has Qs approaching 18 M. These modes are outside the range of acoustic waves in Si, but have non-acoustic bandgaps. The radial mode has a resonance frequency that lies outside the 1.5 MHz wide PnC bandgap. The radial mode has a Q of 750 k. These ultra-high Qs are limited by quantum loss mechanisms, but these materials have lower intrinsic loss than silicon.
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