New Technology Presentation Meetings of Waseda University
Disconnection in wire electrode is automatically repaired by a unique technology

June 21, 2018, “New Technology Presentation Meetings of Waseda University”was held in JST (Tokyo). In this here, two oral presentations are picked up.

Associate professor. Iwase discoursed about wire electrode with self-repaired disconnection and electric device with its electrode. As its name, it is automatic repair technology of disconnection in wire electrode, and effective for a flexible device, which is possible to repeatably vended.

This device is composed of 3 layers, such as, substrate/metal wire electrode/dispersion liquid or gel of Nano size metal grain. In case of occurrence of disconnection in wire electrode, Nano size metal grains aggregate at disconnection area only automatically by applying AC voltage, as a result, disconnection is repaired. This is caused by electric field trap effect, which is generated at disconnection area. In short, it's not necessary to find out place of disconnection. And also, Nano size metal grains don't aggregate in excess, in short, it stop gathering at optimization state, which is almost same thickness as initial thickness. This is reason why electric field trap effect almost disappears because of automatic repair by gathering of Nano size metal grains.

In this experiment, Au electrode and Au Nano size grain (grain size 20 nm) were used. If AC voltage of 1.5 - 3 V is applied, this self-repair process is done. In the past, repair sized was same as 250 nm (width), but in the present moment, it is increased same as 30 μm order. In short, its dimension is sufficient for repair use of wire electrode.

Furthermore, in this process, it's possible to uniform driving voltage of device and repair voltage, too. In this experiment, LED was mounted to a plastic film substrate by wiring electrode. If this sample device was gradually stretched, LED turns off the light from turn-on state because of occurrence of disconnection; on the other hand, after a few seconds, LED turns on again. This is reason why power consumption is consumed for turn-on of LED in normal time, but it is consumed for self-repair process by same voltage automatically and in switching free. In short, if self-repair is completed, LED turns on again and automatically. As a result, it's possible to switch and evaluate automatically.

Comb-shaped electrode was manufactured by use of CNT forest

Instructor. Sugime discoursed about 3D type comb-shaped electrode using Carbon Nano Tube (CNT) forest. In this technology, high density CNT forest is directly grown on the substrate.

With respect to manufacturing process, first of all, Cu conductive layer, Ti contact layer, and Mo/Ti catalyst layer are deposited on the substrate respectively. The next, high density CNT forest is grown on catalyst layer selectively by the CVD method. In this CVD process, CNT forest can be grown at low temperature (500 ℃ and under) for a few minutes.

Effective application is various electrochemical biosensors. In this experiment, a comb-shaped electrode was manufactured due to applying to electrochemical biosensors. Concretely, above electrode and catalyst were deposited, and then, comb-shaped electrode area was patterned by the UV lithography. Subsequently, SiO2 film was deposited and patterned as a masking layer by the lithography, as a result, the upper side of the function electrode 1 and 2 were masked. Finally, CNT was selectively grown on catalyst layer by the CVD method. Its thickness is 0.66 μm. As a result, electrochemical biosensor with high reactive property and thermal resistance property was manufactured. It was confirmed to be advantageous compared to the thermal decomposition carbon type electrode, which is partly put to practical use.