Chemical barriers, isolation devices

This type of isolation device (also called a chemical barrier) is similar to deflagration suppression systems used on process equipment. This barrier system consists of an optical sensor, installed in the pipeline or duct between two items of equipment, that detects an oncoming deflagration... 

Another problem in the construction of these devices, is that materials which do not play a direct part in the operation of the microchip must be introduced to ensure electrical contact between the electronic components, and to reduce the possibility of chemical interactions between the device components. The introduction of such materials usually requires an annealing phase in the construction of the device at a temperature as high as 600 K. As a result it is also most probable, especially in the case of the aluminium-silicon interface, that thin films of oxide exist between the various deposited films. Such a layer will act as a barrier to inter-diffusion between the layers, and the transport of atoms from one layer to the next will be less than would be indicated by the chemical potential driving force. At pinholes in the A1203 layer, aluminium metal can reduce Si02 at isolated spots, and form the pits into the silicon which were observed in early devices. The introduction of a thin layer of platinum silicide between the silicon and aluminium layers reduces the pit formation. However, aluminium has a strong affinity for platinum, and so a layer of chromium is placed between the silicide and aluminium to reduce the invasive interaction of aluminium. 

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