A write-only-read-many (WORM) memory device was obtained by irradiating, with a commercial ultravioletozone (UVO) lamp, the aluminium bottom electrode in an Al/A10(x)-UVO/Al configuration. The formation of conducive paths due Joule heating is observed when a positive or negative bias voltage is applied to the device, occurring a permanent transition from high (OFF) to low (ON) resistance state. After OFF to ON transitions, physical deformations were observed on the top of the devices, which were analyzed using morphological studies of the top electrode. To eliminate these physical deformations, the UVO treatment on the aluminium bottom electrode was replaced by the deposition of a thin polyvinyl alcohol (PVA) film (10 nm). These Al/AlOx native/PVA/Al WORM memories presented similar I-V behaviours and the same threshold voltages to those Al/AlOx-UVO/Al devices, but with higher ON/OFF ratios. Analysis of the I-V curves confirms that the same physical phenomena, such as the formation of filamentary paths, are occurring for both types of devices.