DETERMINATION OF CHARGE-DENSITY AND CHARGE CENTROID LOCATION IN ELECTRETS WITH SEMICONDUCTING SUBSTRATES

A new method for determining the amount and the mean spatial depth of charge in electret-semiconductor systems is presented. It consists of two nondestructive measurements, from which the internal and external electric fields can be calculated independently. Firstly, the surface potential at the electret-air interface is measured by an electrostatic voltmeter. Secondly, using a contacting front electrode, a metal insulator semiconductor structure is formed, on which capacitance or conductance voltage measurements are carried out. With these results, one obtains the surface potential at the electret-semiconductor interface. The charge centroid and the charge density can now be calculated. The method is applied to SiO2 silicon structures, where the 1-mu-m thick thermally wet-grown SiO2 layer acts as an electret. It was found that the charge centroid can be influenced strongly by temperature treatment prior to charging.