top of dielectric layer 520 fig6 shows the same system described above when applied to the definition of the channel on a bottom gate top contact device in this case the metal layer 618 being ablated is on top of semiconductor layer 614 though the above figures show only one opening of the photomask actually the patterning of all metal within the exposure area of the laser ablation system is patterned all at once in this sense laser ablation is a subtractive process requiring that the substrate is coated with the material of choice and is then removed in appropriate areas by laser ablation as defined by a mask in one embodiment a large substrate is covered with a material of choice and with a single ablation exposure defined multiple rfid tags and antennas to create a pattern as shown in fig7 substrate 700 consists of a multiplicity of rfid tags 701 each circuit surrounded by a printed antenna metal 702 it should be noted that the exposure area that a laser system can ablate depends on the size of the optics as well as the total energy needed to ablate the material therefore the rfid circuit must be kept to a dimension in order to accommodate the optics of the laser system and the conductive material should be chosen to have low ablation energy the metal layer can be exposed.