Memory device using quantum dots
A memory device, which includes a memory layer having quantum dots uniformly dispersed in organic material disposed between an upper electrode layer and a lower electrode layer. The memory device is advantageous because it is nonvolatile and inexpensive, and realizes high integration and high speed switching. Further, size and distribution of the quantum dots may be uniform, thus realizing uniform memory behavior. Furthermore, the memory device is suitable for application to portable electronic devices that must have low power consumption, due to low operating voltages thereof.
1. A memory device, comprising:
an upper electrode layer;
a lower electrode layer; and
a memory layer disposed between the upper electrode layer and the lower electrode layer,
wherein the memory layer comprises quantum dots dispersed in an organic material, and
wherein the quantum dots have a core-shell structure, and
wherein the core is conductive and the shell is conductive.
2. The memory device as set forth in claim 1 , wherein the quantum dots are Group II-VI quantum dots, Group III-V quantum dots, or Group IV quantum dots.
3. The memory device as set forth in claim 2 , wherein the quantum dots are selected from the group consisting of CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, GaN, GaP, GaAs, GaSb, AlN, AlP, AlAs, AlSb, InP, InAs, InSb, and SiC.
4. The memory device as set forth in claim 1 , wherein the core-shell structure is a core-shell alloy structure.
5. The memory device as set forth in claim 1 , wherein the core is a Group II-VI compound semiconductor and the core-shell is a Group II-VI compound semiconductor.
6. The memory device as set forth in claim 1 , wherein the size of the quantum dots is from 2 to 10 nm.
7. The memory device as set forth in claim 1 , wherein the organic material is a conductive polymer.
8. The memory device as set forth in claim 7 , wherein the conductive polymer is selected from the group consisting of phenylpolyacetylene polymers, including polydiphenylacetylene, poly(t-butyl)diphenylacetylene, poly(trifluoromethyl)diphenylacetylene, poly(bistrifluoromethyl)acetylene, polybis(t-butyldiphenyl)acetylene, poly(trimethylsillyl)diphenylacetylene, poly(carbazole)diphenylacetylene, polydiacetylene, polyphenylacetylene, polypyridineacetylene, polymethoxyphenylacetylene, polymethylphenylacetylene, poly(t-butyl)phenylacetylene, polynitrophenylacetylene, poly(trifluoromethyl)phenylacetylene, poly(trimethylsillyl)phenylacetylene or derivatives thereof, polypyrroles, polyfurans, polyindoles, polyazulenes, polypyridines, polybipyridines, polyphthalocyanines, poly(3-hexylthiophenes) poly(ethylenedioxythiophenes), and derivatives thereof.
9. The memory device as set forth in claim 7 , wherein the quantum dots and conductive polymer are dissolved in at least one organic solvent to form a coating solution, which is then used for spin coating.
10. The memory device as set forth in claim 1 , wherein the memory layer has a thickness ranging from about 50 to 3000 Å.
11. The memory device as set forth in claim 1 , wherein the memory layer is formed using a spin coating process, an inkjet printing process, a roll-to-roll coating process, or a thermal deposition process.
12. The memory device as set forth in claim 11 , wherein a solvent used for spin coating is selected from the group consisting of acetone, cyclopentanone, cyclohexanone, methylethylketone ethylcellosolveacetate, butylacetate, ethyleneglycol, toluene, xylene, chloroform, tetrahydrofuran, dimethylformamide, acetonitrile, and chlorobenzene.
13. The memory device as set forth in claim 1 , wherein the upper and lower electrode layers comprise a material selected from the group consisting of metals, metal oxides, conductive polymers, and organic conductors.
14. The memory device as set forth in claim 13 , wherein the upper and lower electrode layers include a material selected from the group consisting of aluminum, gold, silver, platinum, copper, titanium, tungsten, and indium tin oxide.
15. The memory device as set forth in claim 1 , wherein the memory device is in a form of a memory matrix.
16. The memory device as set forth in claim 1 , further comprising a barrier layer formed beneath the upper electrode layer, on the lower electrode layer, or both.
17. The memory device as set forth in claim 16 , wherein the barrier layer comprises an inorganic material selected from the group consisting of SiO x , AlO x , NbO x , TiO x , CrO x , VO x , TaO x , CuO x , MgO x , WO x , and AlNO x , or an organic material selected from the group consisting of Alq3, polymethylmethacrylate, polystyrene, and PET.
18. The memory device as set forth in claim 17 , wherein the barrier layer comprises a material selected from the group consisting of SiO 2 , Al 2 O 3 , Cu 2 O, TiO 2 , BN, and V 2 O 3 .
19. The memory device as set forth in claim 16 , wherein the barrier layer has a thickness ranging from about 20 to 300 Å.
20. The memory device as set forth in claim 1 , wherein the upper and lower electrode layers and the memory layer are formed of an organic material.
21. The memory device as set forth in claim 1 , wherein the quantum dots are all substantially uniform in size.
22. The memory device as set forth in claim 1 , wherein the memory layer is configured such that
when a set voltage is applied between the upper and lower electrode layers, a resistance of the memory device is set to a relatively low resistance, and
when a reset voltage is applied between the upper and lower electrode layers, the resistance of the memory device is set to a relatively high resistance, and
wherein a magnitude of the set voltage is less than a magnitude of the reset voltage.
23. The memory device as set forth in claim 22 , wherein the relatively high resistance and the relatively low resistance differ substantially by two orders of magnitude.
24. The memory device as set forth in claim 22 , wherein the magnitudes of the set and reset voltages are substantially 0.25 V and 0.6 V, respectively, or are 0.7 V and 1.2 V, respectively.
25. The memory device as set forth in claim 1 , wherein the core is formed from CdSe and the shell is formed from one or both of ZnS and CdS.
26. The memory device as set forth in claim 1 , wherein the conductive polymer comprises poly(3-hexylthiophene).
27. A memory device using quantum dots, which comprises a memory layer comprising quantum dots dispersed in an organic material disposed between an upper electrode layer and a lower electrode layer,
wherein the organic material is a conductive polymer, and
wherein the conductive polymer is selected from the group consisting of phenylpolyacetylene polymers, including polydiphenylacetylene, poly(t-butyl)diphenylacetylene, poly(trifluoromethyl)diphenylacetylene, poly(bistrifluoromethyl)acetylene, polybis(t-butyldiphenyl)acetylene, poly(trimethylsillyl)diphenylacetylene, poly(carbazole)diphenylacetylene, polydiacetylene, polyphenylacetylene, polypyridineacetylene, polymethoxyphenylacetylene, polymethylphenylacetylene, poly(t-butyl)phenylacetylene, polynitrophenylacetylene, poly(trifluoromethyl)phenylacetylene, poly(trimethylsillyl)phenylacetylene or derivatives thereof, polypyrroles, polyfurans, polyindoles, polyazulenes, polypyridines, polybipyridines, polyphthalocyanines, poly(3-hexylthiophenes) poly(ethylenedioxythiophenes), and derivatives thereof.
28. The memory device as set forth in claim 27 , wherein the conductive polymer comprises phenyl polyacetylene.
29. The memory device as set forth in claim 27 , wherein the conductive polymer comprises poly(3-hexylthiophene).