Power device, diamond

Diamond can be deposited as a coating on refractory metals, oxides, nitrides, and carbides. For maximum adhesion, the surface should be a carbide-forming material with a low TCE. Diamond has an extremely high thermal conductivity, several times that of the next highest material. The primary application is, obviously, in packaging power devices. Diamond has a low specific heat, however, and works best as a heat spreader in conjunction with a heat sink. For maximum effectiveness, ... 

One of the major markets for wide band-gap materials is in electronics. Specifically, they are suitable for and have been used for heat sinks (diamond), short wavelength optoelectronic devices (GaP, GaN, SiC), high-temperature electronics (SiC, GaN), radiation resistant devices, and high-power/high-frequency electronic devices (diamond, GaN, SiC). " Recent research showed that Mn-doped GaN can be used for spintro-nic applications.f" Atomically flat technology developed by NASA for SiC and GaN WBG material can introduce a new dimension of application for WBG materials. 

As can be seen from the figure of merit in Table 1, diamond fulfills the expectations for power devices from various points of view, unless the technologies are not mature at present. One of the problems with diamond at this stage is that only p-type doping is possible with boron. For varieties of devices and integrated circuits, n-type diamond is preferable, but this is not inevitable because in most cases unipolar devices are possible. 

Diamond and Refractory Ceramic Semiconductors. Ceramic thin films of diamond, sihcon carbide, and other refractory semiconductors (qv), eg, cubic BN and BP and GaN and GaAlN, are of interest because of the special combination of thermal, mechanical, and electronic properties (see Refractories). The majority of the research effort has focused on SiC and diamond, because these materials have much greater figures of merit for transistor power and frequency performance than Si, GaAs, and InP (13). Compared to typical semiconductors such as Si and GaAs, these materials also offer the possibiUty of device operation at considerably higher temperatures. For example, operation of a siUcon carbide MOSFET at temperatures above 900 K has been demonstrated. These devices have not yet been commercialized, however. 

It is well recognized that CVD diamond would be the ideal material for many semiconductor applications, particularly in high power and high frequency systems such as microwave, as well as in harsh environments, such as in internal combustion and jet engines. However, many problems must be solved before practical, reliable, and cost-effective diamond semiconductor devices can be produced. 

Some of the present industrial uses of diamond coatings include cutting tools, optical windows, heat spreaders, acoustic wave filters, flat-panel displays, photomultiplier and microwave power tubes, night vision devices, and sensors. Because its thermal conductivity and electrical insulation qualities are high, diamond is used for heat sinks in x- ray windows, circuit packaging, and high-power electroific devices. Moreover, the high chemical stability and inertness of diamond make it ideal for use in corrosive environments and in prosthetic devices that require biocompatibility. 

Chemical vapor deposition films have been grown on an Ir/SrTiOs substrate of around 0.6 cm for a field effect transistor application achieving for the first time an RF output power for a device operating at frequencies of the order 10 Hz. Larger-size substrates will eventually allow the development of power diamond transistors at wafer scale. ... 

The record-high thermal conductivity of diamond makes it an obvious choice for consideration as a substrate for high power electronic devices. One method that has been successful in producing diamond films is chemical vapor deposition (CVD). The CVD diamond films are polycrystalline, but can still have k > 2000Wm" K . The high cost of diamond films still precludes their widespread use. 

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