A positive temperature coefficient ceramic thermistor element includes a sintered thermosensitive ceramic piece that uses lead barium titanate as a base, as well as metal ohmic electrodes which are positioned on two side surfaces of the thermosensitive ceramic piece. The thermistor element has a microporous channel barrier layer, and includes a glass sealing layer which wraps the outer surface of the thermosensitive ceramic piece, or an organic matter sealant which fills and blocks micro-pores in the surfaces of the metal ohmic electrodes combined on the two side surfaces of the thermosensitive ceramic piece and, at the same time, blocks gaps in the surfaces of areas, that do not have the metal ohmic electrodes, of a peripheral edge of the thermosensitive ceramic piece.

A preparation method for a copper plate-covered silicon nitride ceramic substrate is provided. The structure of the copper plate-covered silicon nitride ceramic substrate includes a silicon nitride ceramic substrate, copper sheets disposed on the upper and lower sides of the silicon nitride ceramic substrate and soldering layers disposed between the copper sheets and the silicon nitride ceramic substrate; the composition of the silicon nitride ceramic substrate comprises a silicon nitride phase (more than or equal to 95 wt %); and a grain boundary phase (containing at least three elements (Y, Mg and O) and less than or equal to 5 wt %, and the content of a crystalline phase in the grain boundary phase is more than or equal to 40 vol %); and the sintering aids are Y.sub.2O.sub.3 and MgO. The two-step sintering process comprises: in a nitrogen atmosphere, performing low-temperature heat treatment and high-temperature heat treatment in sequence.

The invention relates to a process for producing a metal-ceramic substrate (1), comprising: providing a ceramic element (10), a metal ply (40) and at least one metal layer (30), forming an ensemble (18) of the ceramic element (10), the metal ply (40) and the at least one metal layer (30), forming a gas-tight container (30) surrounding the ceramic element (10), wherein the at least one metal layer (30) is arranged between the ceramic element (10) and the metal ply (40) in the container, andforming the metal-ceramic substrate (1) by hot isostatic pressing.

In embodiments a method for providing a contacting for a functional ceramic element includes providing a functional ceramic, applying a metal paste to two opposing surfaces of the functional ceramic, laminating ceramic substrate green films on the metal paste on the two opposite surfaces of the functional ceramic, and jointly sintering the functional ceramic, the ceramic substrate green films forming electrically insulating ceramic layers and the metal paste forming electrically conductive metal structures.