Machinable Aluminium Nitride Uses in Piezoelectric Transducers
Machinable aluminium nitride has found a use in ultrasound technology for fingerprint scanning.
Machinable aluminium nitride is one of the specialist technical ceramics that can be used for a variety of extremely demanding applications. This is the compound that not only has the highest thermal conductivity of any non-metal, but its thermal conductivity is also akin to that of many metals. It is also an efficient electrical insulator.
This is why it is used as a heat sink in in many lighting, optics and microelectronic devices. It remains stable up to about 1,000 degrees C in the atmosphere and to 1,900 degrees C when placed in an inert gas. In addition, its coefficient of thermal expansion is comparable to both aluminium oxide and aluminium metal.
However, it is the use of machinable aluminium nitride in piezoelectric transducers that it is the latest technological leap. A thin film of aluminium nitride is used as a coating on a semiconductor ship. When subjected to any mechanical stress, this coated chip converts the mechanical force into electricity. The reverse is also true: this ceramic converts electricity into a mechanical force
This is where fingerprint scanning comes in. The principle of an electrical fingerprint scanner is to recognise the valleys and ridges of a given fingerprint by mapping them when a finger presses against a scanner screen. The piezoelectric properties of the coated chip sensor produce different kind of electrical voltages depending on whether it senses a ridge or a valley.
The problem is that such a scanner’s efficiency may deteriorate with time as grease and dirt become locked into the devices. So ultrasound technology has been adopted to ensure the scanners do not malfunction.
The chip coated with machinable aluminium nitride inside the scanner is used to emit an ultrasound pulse. When a finger is placed on the scanner, the pulse will bounce back and then be converted into electricity. The finger remains on the scanner over a long period of time to enable the scanner to generate a 3-D picture of valleys and ridges. As the resulting 3-D image provides the deep characteristic of a fingerprint as well as its 2-D shape, it becomes a more accurate identification device.
Lead zirconate titanate has been used previously as the chip coating ceramic, but it presented many manufacturing difficulties. Machinable aluminium nitride is a more convenient ceramic to work with.
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