Organic-inorganic heterojunction WORM memory

Xin Xu

A simple, non-volatile, write-once-read-many-times (WORM) memory device can be formed by an organic-inorganic hetero-junction (OI-HJ) diode with a conductive polymer fuse. The polyethylene dioxythiophene: polysterene sulfonic acid (PEDOT: PSS) and the inorganic semiconductor are expected to form a rectifying junction. Current transients are applied to change the fuse from conductive to un-conductive state to record a logical 1 and 0, while the rectifying character of the OI-HJ allows for passive matrix memory addressing.

Although the idea and the corresponding switching of PEDOT: PSS have already been demonstrated, the underlying mechanism of PEDOT: PSS switching and the properties of organic-inorganic interface are still not obvious. In this work, we are attempting to gain a fundamental understanding of conducting polymers and the transport of charge across the organic-inorganic heterojunction, which is important to the implementation of these hybrid structures in practical memories.

Figure 1. The I-V curve of an OI-HJ memory element is shown. The device is with the structure of n-Si/PEDT:PSS/Au. Pulses with different duty cycles are provided and correspondingly, in each situation there is a current peak showing a permanent switching of the polymer. For this case, the baking temperature to remove the water residual in polymer is 140oC and the device is under forward bias which means a positive potential is applied to Au contact while the substrate is connected to the ground.

References:

Moller, S; Perlov, C; Jackson, W; Taussig, C; Forrest, SR. A polymer/semiconductor write-once read-many-times memory. Nature 426 (6963): 166-169 (2003).

Moller, S; Forrest, SR; Perlov, C; Jackson, W; Taussig, C. Electrochromic conductive polymer fuses for hybrid organic/inorganic semiconductor memories. Journal of Applied Physics 94 (12): 7811-7819 (2003).

Smith, S: Forrest, SR. A low switching voltage organic-on-inorganic heterojunction memory element utilizing a conductive polymer fuse on a doped silicon substrate. Applied Physics Letters 84 (24): 5019-5021 (2004).