Semiconductor device and fabrication method

An IC card comprising:

• a flexible upper card substrate,
• a flexible lower card substrate to be bonded with the upper card substrate for structuring an IC card substrate, wherein the thickness of the lower card substrate is substantially the same as the thickness of the upper card substrate, and
• a thin-film semiconductor device having at least a semiconductor element and wiring, and a thin film of a protective insulating material formed on the lower surface of said semiconductor element, wherein said thin-film semiconductor device is placed between the upper card substrate and lower card substrate to be located on a neutral plane of the IC card,
• wherein the thickness of the thin-film semiconductor device and the thickness of the IC card are set at a predetermined ratio relative to one another such that the thickness of the thin-film semiconductor device is a finite value of not greater than 19 microns for the IC card having thickness of equal to or greater than 500 microns.

An IC card comprising:

• a flexible upper card substrate,
• a flexible lower card substrate to be bonded with the upper card substrate for structuring an IC card substrate, wherein the thickness of the lower card substrate is substantially the same as the thickness of the upper card substrate, and
• a thin-film semiconductor device having at least a semiconductor element and wiring, and a thin-film of a protective insulating material formed on the lower surface of said semiconductor element, wherein said thin-film semiconductor device is placed between the upper card substrate and lower card substrate to be located on a neutral plane of the IC card;
• wherein the thickness of the thin-film semiconductor device and the thickness of the IC card are set at a predetermined ratio relative to one another such that the thickness of the thin-film semiconductor device is a finite value of not greater than 4 microns for the IC card having a thickness equal to greater than 250 microns.

An IC card comprising:

• a flexible upper card substrate,
• a flexible lower card substrate to be bonded with the upper card substrate for structuring an IC card substrate, wherein the thickness of the lower card substrate is substantially the same as the thickness of the upper card substrate, and
• a thin-film semiconductor device having at least a semiconductor element and wiring, and a thin film of a protective insulating material formed on the lower surface of said semiconductor element, wherein said thin-film semiconductor device is placed between the upper card substrate and lower card substrate to be located on a neutral plane of the IC card, and
• wherein a thickness ratio between said IC card substrate and said thin-film semiconductor device is less than 110/760.

An IC card made by a process comprising the steps of:

• preparing a flexible upper card substrate and a flexible lower card substrate to be bonded with the upper card substrate for structuring an IC card substrate, wherein the thickness of the lower card substrate is substantially the same as the thickness of the upper card substrate, and wherein the thickness of said IC card substrate is not greater than 760 microns;
• preparing a thin-film semiconductor device on a main surface of silicon-on-insulator element, having at least a semiconductor element and wiring, wherein the thin film semiconductor device has a thickness not greater than 110 nm;
• stripping said thin-film semiconductor device off said main surface of said silicon-on-insulator element;
• forming a thin film of a protective insulating material on the lower surface of said semiconductor element;
• adhering said thin-film semiconductor device onto said lower card substrate;
• and
• adhering said upper card substrate onto the lower card substrate on the surface where the thin-film semiconductor device is adhered so that the thin-film semiconductor device is placed in a neutral plane of the IC card substrate.