Technology implantable

Tra.nsitorAmplifiers. Most gaUium-based field-effect transitor amplifiers (FETs) are manufactured using ion implantation (qv) (52), except for high microwave frequencies and low noise requirements where epitaxy is used. The majority of discrete high electron mobiHty transistor (HEMT) low noise amplifiers are currently produced on MBE substrates. Discrete high barrier transistor (HBT) power amplifiers use MOCVD and MBE technologies. 

Dielectric Film Deposition. Dielectric films are found in all VLSI circuits to provide insulation between conducting layers, as diffusion and ion implantation (qv) masks, for diffusion from doped oxides, to cap doped films to prevent outdiffusion, and for passivating devices as a measure of protection against external contamination, moisture, and scratches. Properties that define the nature and function of dielectric films are the dielectric constant, the process temperature, and specific fabrication characteristics such as step coverage, gap-filling capabihties, density stress, contamination, thickness uniformity, deposition rate, and moisture resistance (2). Several processes are used to deposit dielectric films including atmospheric pressure CVD (APCVD), low pressure CVD (LPCVD), or plasma-enhanced CVD (PECVD) (see Plasma technology). 

The physical techniques used in IC analysis all employ some type of primary analytical beam to irradiate a substrate and interact with the substrate s physical or chemical properties, producing a secondary effect that is measured and interpreted. The three most commonly used analytical beams are electron, ion, and photon x-ray beams. Each combination of primary irradiation and secondary effect defines a specific analytical technique. The IC substrate properties that are most frequendy analyzed include size, elemental and compositional identification, topology, morphology, lateral and depth resolution of surface features or implantation profiles, and film thickness and conformance. A summary of commonly used analytical techniques for VLSI technology can be found in Table 3. 

Although there has been theoretical and experimental interest in the effects of ion bombardment on materials since about 1960 (153), the growth in ion implantation technology and appHcations since then is due almost solely to the semiconductor (integrated circuit) industry. The advantages of ion implantation for semiconductor doping were first pointed out in 1955 (154), but these advantages were not widely accepted until about 1970. 

J. E. Ziegler, ed.. Handbook of Ion Implantation Technology, North-HoUand, New York, 1992. 

Bicomponent technology has been used to introduce functional and novelty effects other than stretch to nylon fibers. For instance, antistatic yams are made by spinning a conductive carbon-black polymer dispersion as a core with a sheath of nylon (188) and as a side-by-side configuration (189). At 0.1—1.0% implants, these conductive filaments give durable static resistance to nylon carpets without interfering with dye coloration. Conductive materials such as carbon black or metals as a sheath around a core of nylon interfere with color, especially light shades. 

One of the more intriguing cardiovascular developments is cardiomyoplasty where implantable technologies are blended with another part of the body to take over for a diseased heart. One company, Medtronic, in close collaboration with surgeons, has developed a cardiomyoplasty system to accompany a technique of wrapping back muscle around a diseased heart which can no longer adequately pump. A combination pacemaker and neurological device senses the electrical activity of the heart and correspondingly trains and stimulates the dorsal muscle to cause the defective heart to contract and pump blood. Over 50 implants have been performed to date. 

Hydroxyapatite (HA) coating on the surface of the hip stem and the acetabular cup is the most recent advancement in artificial hip joint implant technology. This substance is a form of calcium phosphate, which is sprayed onto the hip implant. It is a material found in combination with calcium carbonate in bone tissue, and bones can easily adapt to it. When bone tissue does grow into HA, the tissue then fixes the hip joint implant permanently in position. These HA coatings are only used in press-fit, noncemented implants. 

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