[ODCAD] Organic Memory with Cu(TCNQ) as Active Layer

Cu(TCNQ) is organometallic material. Organic compound TCNQ has CN group that is good electron acceptor, and form charge transfer complex (CT) with Cu.  There is a set of this type material. They are Cu(TCNE), Cu(TCNAP), Cu(DM-TCNQI).   The conductivity of the material can be manipulated by applying voltage. A structure Cu/Cu(TCNQ)(5~10um)/Cr can be switched from off to On with conductivity change over 100 times when V>Vt~3V. This switch is independent of voltage polarity.  The "On" state stays even after removing  the field.  This memory effect has data retention up to days.  The "on" state can be switched "off" after applying opposite voltage on the device. There are two models to descibe the switching mechanism. Model 1 is Field Induced Electrochemical Reaction.     Cu(TCNQ)  <=> Cu + TCNQ Off state has more Cu(TCNQ) that is thermodynamically more favored.  With the help of field, Cu gains electron back and the mixture Cu+TCNQ is more conductive. This state is less stable and can change back to Cu(TCNQ) either after certain time or with opposite field. A  recent work [1] suggests that the switch is due to Phase change.  CU(TCNQ has two phases. Phase 1 has Cu bonded with two sets of TCNQ in two perpendicular planes.   Phase II has Cu bonded with all TCNQ in almost on teh same plane. Therefore, this allows more dilocalized space for conductive electrone.  Concequently, Phase II has higher conductivity.  This work reports that the phase II has conductivity upto 1000 S/cm, and Phase 1 has conductivity 1.0E-5 S/cm.  The phase I is more stable and can be switched to phase II by external field, and this state can be changed back by opposite field.   1. R. A. Heintz, H. Zhao, X. Ouyang, G. Grandinetti, J. Cowen, and K. R. Dunbar; Inorg. Chem.; 38, 144 (1999) 2. R. S. Potember, T. O. Poehler; Semiconducting Organic Thin Films; 17, 233 (1982) 3. R. S. Potember, T. O. Poehler; Appl. Phys. Lett.; 34, 405 (1979)

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[ODCAD] UCLA's organic memory-mechanism

A UCLA material scientist, Yang Yang discovered a simple organic memory device. A patent [1] has been filed to protect this IP because it has great potential to be applicable to the industry.

This device manufacture and operation has been described in previous topic "UCLA-a Simple organic memory". The latest result from Yang Yang's work [2] shows that the "on" state is not filament. This is because the "ON" state conductivity is proportional to the cross section area of device. The on conductivity is an increase function of temperature. This indicate that the on state is not "metal" state.

AFM image shows that the middle Al layer in the device (Al/Organic/Al/Organic/Al) has b nano crystal structure. X ray spectroscopy demonstrated that this nano crystal may be in form of oxide. The oxide may be formed due to exposed to air. It would be interested to see what behavior the device has if the middle Al is in metal form.
UV-visible absorption spectra can see that the middle layer Al quality gives significant difference in terms of its structure. Al deposited at slow rate can give high yield of the device.

These observations indicate that the Al oxide in the middle layer function as charge carrier trap. After switched on, the injected charge carrier are trapped. Therefore, the conductivity has been significantly increased.

It would be more convincing if proper energy level is used for explaining the trap mechanism. The Al is in nano cluster form. The bulk Al energy level can not be applied here. Possibly there are quantum wells produced by the crystal cluster. It would be a great research topic for scientist.


1. US pending patent US 01/17206 (2001)
2. L. Ma, S., Pyo, J. Ouyang, Q. Xu, Y. Yang, Appl. Phys. Lett., 82, 1419 (2003)
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[ODCAD] Ferroelectric polymer: Memory device material

A molecule with polar component may have ferroelectric behavior.
Timothy, a scientist from Univ. of Nebraska has used a polymer
polyvinylidene (TrFE) as function layer in his memory device. The
ferroelectric property of the molecule in crystal does give a good
memory behavior in its I-V curve. The material can sustain high tecm
upto 450 C for 10 min. Therefore, it can be mixed with conventional
Si technology. Reference Appl. Phys. Lett., 82, 142 (2003)

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[ODCAD Comment] HP Lab: Organic WORM Memory
HP Lab and Electrical Engineering Dept., Princeton Univ. have teamed up to use polymer semiconductor PEDOT as active material for write-once-read-many-times (WORM) device.

Regular PEDOT is semiconductor. However, its conductivity can be changed into insulating when enough current is put through the material. The blown fuse, then can be read as a zero and an intact fuse as a one. The bit memory cell has size 100-200 nanometer.

Stack up layered structure is possible to achieve high density /area. It could be cheap because it may not require clean-room environment. It is not clear if photolithography is required.

It can be fast since the technology reads each bit by current instead by moving head.

Disadvantage is that the cell size may have difficulty to scale down further.

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