Initial Charge in polymer film

This figure is a space charge distribution in a polymer film including initial charge which could be formed during the manufacturing process.

The charge remains when I filed the surface with a sand paper! The top waveform shows the original, and (b), (c),...shows the internal charge of the filed sample. Each thickness is shown at the bottom of the figure. The charge can disappear when it's heated up to Tg.

Ion conductive polymer

These signals are the charge distributions in an ion conductive polymer; called as 'antistatic polymer', obtained under dc electric field.
When the polymer contains a type of solid electrolyte in 5 %, only the surface charges appear on the both electrodes, as shown in the tope green signal. It is as same as that in a normal acrylin resin.
In the cases of 30 % or more, internal positive charges can move and accumulate at the interface between the sample and the cathode. This phenomena has been explained that the polymer solid electrolytes formed the network inside the matrix polymer.

Organic photoconductor

We have experimentally investigated the internal space charge behaviour of a charge transport layers (CTL) of an organic photoconductor (OPC) when different electrode are used to inject charge. Injected positive charge (holes) moves through the CTL, and accumulates at this interface. The results indicate that the hole injection from an anode is influenced by the type of the electrode materials.

Printed circuit boards

It is well known that ion migration occurs before the breakdown of a printed circuit board (PCB), but the word 'migration' usually implies 'surface migration' which makes circuits be short-circuited. In the case of a metal-based PCB, migration occurs inside the insulation layer. We measured the space charge behaviour in PCBs, and investigated whether or not the space charge measurement is effective in determining the cause of ion migration. The copper distributions are clearly observed in these aged samples, and the regions are exactly the same as the highly conductive region obtained by the space charge measurements.

As iom migration occurs in three dimensions, 3-D space charge observation gives more useful information about it. We observed a specimen that has copper ion migration, similar to the example above. When a positive dc voltage was applied to the anode, the positive signal appeared inside the epoxy resin, and deeper around the edge. It is becuase the electric field around the edge was higher than other area, and then the migration can grow faster.

Materials for space industry

The PEA unit has been mounted in an irradiation chamber at ONERA-CERT (Toulouse, France). Experimental results suggest that the space charge profiles are clearly observed during or after irradiation (accumulation and decaly of charges). The combination of in situ observation of the surface potential and the internal space charge behaviour can give valuable information to investigate the materials used in the space environment.

-- Works introduced in this website has been done at NICT. --

(Last Update: August, 2004)