the particular processes for forming the various layers and elements of the printhead assembly according to the invention will be described in the order in which these fabrication processes are followed in the construction of the device the deposition processes operate in the pressure range of about 2 torr or less the thermal insulating barrier 4 of silicon dioxide may be formed by either of two techniques the layer may be a deposited film of silicon dioxide or it may be a grown layer the grown form of silicon dioxide is accomplished by heating the silicon substrate itself in an oxidizing atmosphere according to techniques well known in the art of semi conductor silicon processing the deposited form of silicon dioxide is accomplished by heating the silicon substrate 2 in a mixture of silane oxygen and argon at a temperature of from 300 to 400 degrees c until the desired thickness of silicon dioxide has been deposited the polycrystalline layer 6 may be formed by the plasma enhanced chemical vapor deposition of silicon by the decomposition of a silicon compound such as silane diluted by argon a typical temperature to achieve this decomposition and deposition is 500 to 600 degrees centrigrade for example and a typical deposition rate is about one micron per minute the resistive element 8 may be formed by the diffusion of phosphorus into the polycrystalline silicon layer 6 using oxide masking and diffusion techniques well known in the art of.