Types of dielectric layers

As mentioned briefly above there are many dielectrics in use  

It is well established that the degree of selectivity can vary extremely going from one dielectric to the other [Chow et al.67, Broadbent et al.131, Chow et al.133, Bradbury et al.134, Wilson et al.135]. Silicon nitride, for instance, is notorious for its low selectivity whereas phosphorous doped glasses show an improved selectivity compared with undoped glasses (see also section 3.5). 

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