We report a nonvolatile, write-once-read-many-times (WORM) memory device based on a simple organic-inorganic heterojunction. The organic-based hybrid used is 9,9-dihexylfluorene and Eu-complexed benzoate, which contains both electron-donor (9,9"-dihexylfluorene) and electron-acceptor (europium complex) groups. Under current-voltage testing, the device is able to switch from one initial nonconducting state to a conducting state once a threshold voltage is reached. Diode rectifying characteristics, with a current ratio of four orders of magnitude, is also observed after the device is turned on, which is essential to address one memory cell in large passive matrix circuits.

The molecular conformation-dependent write-once read-many-times (WORM) memory based on an acrylate polymer containing pendant carbazole (donor) groups is transformed into a flash (rewritable) memory when acrylate units containing pendant oxadiazole (acceptor) groups are incorporated to form a copolymer. The as-fabricated device based on the acrylate copolymer containing carbazole-oxadiazole donor-acceptor pendant groups is in its low conductivity state and can be written to a high conductivity state at a threshold voltage of -1.8 V. The high conductivity state can be switched (erased) to the low conductivity state with a positive bias of 3.6 V. The device exhibits a high ON/OFF current ratio of 103 at a read voltage of -1 V. This rewritable polymer memory can be programmed and erased repeatedly with good accuracy. The copolymer is potentially useful for application in flash memory devices.

We present an electrical-bistability device based on MIM-sandwiched structure. Poly(N-vinylcarbazole) (PVK) mixed with gold nanoparticles (GNPs) serve as the active layer between two metal electrodes. After applying a voltage, the as-fabricated device can transit from low conductivity state to high conductivity state. By simply using a reverse bias, the high conductivity state can return to the low conductivity state. An ON/OFF current ratio as high as 10(5) at room temperature has been achieved. The memory effect is attributed to electric-field-induced charge transfer complex formed between the PVK and the GNPs. The device shows a good stability under stress test for both states and exhibits a high potential on Flash-type memory applications.

A write-once read-many-times (WORM) memory device based on an acrylate polymer containing electron donating carbazole pendant groups, or poly(2-(9H-carbazol-9-yl)ethyl methacrylate) (PCz), was demonstrated. The as-fabricated device was found to be at its OFF state and could be programmed irreversibly to the ON state. The WORM device exhibited a high ON/OFF current ratio of up to 106, a long retention time in both ON and OFF states, a switching time of 1ms, and number of read cycles up to ∼107. Compared to that of poly(N-vinylcarbazole) (PVK), the well-defined memory property of PCz can be attributed to the presence of the spacer between the pendant carbazole group and the polymer backbone. The molecular spacer has allowed the transition of the pendant carbazole groups from the disoriented state to the ordered face-to-face conformation at the threshold voltage.

A conjugated copolymer of diethylhexylfluorene and europium complex-chelated benzoate (PF8Eu) was synthesized. The device based on an Al/PF8Eu/indium-tin-oxide sandwich structure exhibited nonvolatile, write-once read-many-times (WORM) memory behavior. The fluorene moiety served as the backbone and electron donor, while the europium complex served as the electron acceptor. The as-fabricated device was in its low conductivity state. After applying a voltage of ∼3V, the device underwent a transition to the high conductivity state, which could not be erased by a reverse bias. In the initial low conductivity state, the device showed a charge injection controlled current. At the high conductivity state, the current-voltage characteristics were dominated by a space-charge-limited current. The device had a switching time of ∼1μs and an on/off current ratio as high as 106. No degradation in device performance was observed after 107 read cycles at a read voltage of 1V under ambient conditions. The device also exhibited good stability under a constant 1V stress. Thus, the device based on PF8Eu is potentially useful as a WORM memory.