Ebook Diamond semiconductor technology for RF device applications
Diamond, known for more than 200 years, has been a dream for the device engineers due to its unique material properties. It was identified as carbon in 1796, but synthesized in 1954. The main reason behind this is the difficulties to exploit these properties due to the cost and scarcity of large natural diamonds, and the fact that diamond was only available in the form of stones or grit. To overcome these problems, researchers realized that in order to form diamond, conditions are needed where diamond is in a more stable phase. The chemical vapor deposition (CVD) of diamond is one of the most popular, technically well understood and established, as well as commercially viable methods for synthesizing diamond. The first reproducable synthesis of artificial diamond, using a process requiring high temperature and high pressure was reported by General Electric Company in 1955. CVD was then used for the first time for synthesizing diamond by Eversole in 1962.
CVD is a process in which gaseous precursors are introduced into a reactor and a solid is deposited on a usually hot substrate due to chemical reactions between the precursors. CVD is an atomistic process, in that the coat grows molecule by molecule. The consequence is that the process is slow and coatings are thin, but the result is a dense high quality deposit with good adhesion to the substrate due to atomic bond formation. Conventionally, the substrate is thermally activated to initiate the CVD reaction, typically above 800 °C. This could also be a serious limitation to some less stable sub-strates. Alternative activation techniques have recently become available which can effectively lower the reaction threshold temperature to $100 °C. These are laser-assisted CVD (LCVD), plasma-activated CVD (PACVD) and electron beam induced CVD (EBCVD). All CVD techniques for producing diamond films require a means of activating gas-phase carbon-containing precursor molecules. This generally involves thermal (e.g. hot filament) or plasma (DC or RF) activation, or use of a combustion flame (oxyacetylene or plasma torches). While each method differs in detail, they all share features in common. A detailed study on CVD diamond process and films is already done by Railkar
et al.
CVD diamond has properties that are very similar to those of natural diamond and yet it can be made in the form of large freestanding sheets that is extremely important for electronic applications such as substrates and heat spreaders. Beside such passive devices, CVD diamond has numerous attractive physical and electrical properties for active device applications, especially RF power electronics. The wide band gap, small (or negative) electron affinity, high breakdown voltage, high saturation drift velocity, high carrier mobility, radiation hardness and high thermal conductivity make diamond a promising material for fabrication of high power, high frequency and high temperature solid-state microelectronic devices, sensors/MEMS and vacuum microelectronic devices (e.g. field emission devices). The exceptional material properties of diamond is summarized in Table 1. A large number of research groups and manufacturers all over the world are currently working on different applications relevant to diamond.
From RF applications perspective, our study first demonstrates the material issues and technological challenges related to diamond; then we examine the potentials of diamond under these technological challenges, discover the key features of each device type or application and illustrate the simulation results based on our survey for comparison with theoretical aspects. We finally discuss the current status and expectations as well as future trends of diamond-based RF device technology.
Contents
1. Introduction
2. Material issues and technological challenges
3. Diamond RF electronics
- 3.1. Diamond based diodes
3.2. Diamond BJT
3.3. Diamond FETs
- 3.3.1. Boron d-doped channel FETs
3.3.2. Surface channel FETs
3.4. Diamond RF MEMS
3.5. Diamond-based surface acoustic wave (SAW) devices
3.6. Diamond field emission devices
3.7. Thermal management with diamond devices
3.8. Performance summary of diamond RF devices
4. Summary and future trends
Acknowledgements
References
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