Abstract: Injection and proportioning head with at least one thermal injection and proportioning device to supply a determined quantity of liquid, comprising: a hollowed out plane substrate (21) forming a liquid reservoir and covered, in order, by an unconstrained dielectric insulating membrane (22, 23) with a high thermal resistance, and then an etched semi conducting layer forming the heating resistance (25); an orifice (24) enabling fluid communication with said liquid reservoir passing through said membrane and said semi conducting layer; a photolithographed resin layer in the form of a nozzle (27) on said membrane, the duct (28) of said nozzle being in line with said orifice and the volume of said duct being such that the determined quantity of the liquid to be supplied can be controlled. Process for manufacturing this head. Functionalisation or addressing system, particularly for chemical or biochemical micro reactors comprising this head.