Non‐Volatile Organic Memory Applications Enabled by In Situ Synthesis of Gold Nanoparticles in a Self‐Assembled Block Copolymer

Abstract

Block copolymers have unique associative properties that facilitate self-assembly into nanostructures that have been widely used in soft lithography, [1] templating, [2] drug delivery, [3] biomedical, [4,5] and chemical catalytic [6] applications. Of special interest is the in situ preparation of metallic or semiconducting nanoparticles in amphiphilic block copolymers. [7][8][9][10][11][12] The synthesis of nanoparticles in block copolymer micelles solves the problem of particle size control and stabilization compared to classical stabilization systems that employ surfactants [13][14][15] or microemulsions. [16,17] Nanocrystal-based organic memories [18][19][20][21] are attracting widespread interest owing to their simple structure and the prospect of creating 2D/3D stacks of these memory cells for increased bit densities. Recent reviews [20,22,28] summarize the literature for these nanoparticle-based organic memories comprehensively, and have identified the main operating mechanisms to be one of the following: (i) an electricfield-induced charge transfer between the nanoparticles and the surrounding conjugated compounds, [19,22] (ii) filamentary conduction, [23,24] (iii) charge trapping-detrapping, [25,26] and (iv) space-charge field inhibition of injection in the nanoparticles through a high-voltage pulse. [20,27] Besides the widely used two-terminal bistable organic memory devices, an alternative memory architecture that can be adopted is based on an organic thin-film transistor (OTFT) with a non-volatile floating gate memory [29] which allows a direct integration of the memory element with the transistor for integrated circuit applications. The ability to have a one-step fabrication process to generate arrays of metallic nanoparticles using solutionprocessing methods makes this approach amenable to potential implementations in the nanoparticle-based organic memory devices mentioned above. This is in contrast to past designs of organic memory devices, which involved the use of multistep approaches of presynthesizing nanoparticles followed by surface modification to prevent agglomeration prior to embedding them in multiple functional layers through solution processing or physical vapor deposition. Furthermore, this solution-processing approach is especially suitable for low-cost, large-area processing on flexible substrates, which may be considered to be the cornerstone of organic electronics applications. We demonstrate herein, for the first time, a polymeric memory that comprises an in situ synthesis strategy of gold nanoparticles in polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP). This system serves as a prototype for a generic memory device using nanoparticles as floating gate charge storage centers and, in particular, for integration into OTFT-based circuits. The block copolymer micelles turn out to be an excellent model system that is simple, forms a self-assembled ordered nanostructure, and provides optimum control over nanoparticle size formation and isolation. The response of the memory device is c...

Recent progress in gold nanoparticle-based non-volatile memory devices

“…After the fabrication of source-drain junctions and gateelectrode definition, MOSFET-structure memory devices were fabricated. The average size of gold diblock copolymer micelles to synthesize gold nanoparticles in MOS-capacitor memory devices, but P4VP core and PS corona block copolymers were not removed since PS and P4VP could be used as the potential well of gold nanoparticles in memory device structures [48]. In addition, there was a report nanoparticles was around 5 nm and the density was around 5×10 12 cm -2 .…”

Nonvolatile organic transistor-memory devices using various thicknesses of silver nanoparticle layers

“…Recently a 26ϫ 26 array of organic flash memory transistors based on floating gate structure was demonstrated on flexible plastic sheets, and the operating voltage was as low as 6 V. 3 Currently, different approaches have been adopted to fabricate organic nonvolatile memory devices, such as using ferroelectric polymer dielectric materials 4,5 and chargeable gate dielectric in the organic field-effect transistors ͑OFETs͒. 6 In these devices, the memory effect arises from the field effect modulation by either the spontaneous polarization that occurs in ferroelectric, or through the trapping of charges in a chargeable layer of the dielectric. 7 Usually, the charge-trapping elements in the chargeable gate dielectric are nanoparticles ͑NPs͒ of metals such as Cr, 8 Au, 6 and Ag.…”

“…6 In these devices, the memory effect arises from the field effect modulation by either the spontaneous polarization that occurs in ferroelectric, or through the trapping of charges in a chargeable layer of the dielectric. 7 Usually, the charge-trapping elements in the chargeable gate dielectric are nanoparticles ͑NPs͒ of metals such as Cr, 8 Au, 6 and Ag. 9 Compared with ferroelectric polymer-based memory, devices using metal NPs as charge traps have an advantage that the trap density and distribution can be controlled by adjusting the density and location of the NPs during the NP formation process, by using ultrathin metallic films deposition or ion implantation techniques.…”

Phthalocyanine‐Cored Star‐Shaped Polystyrene for Nano Floating Gate in Nonvolatile Organic Transistor Memory Device

“…This result indicates that the limited number of hole charges are trapped in the CuPc-PS 4 gate vias. [ 20,21,42 ] The maximum memory I ON / I OFF ratio between programmed and erased states was over 10 7 owing to the large intrinsic I ON / I OFF ratio of the CuPc-PS 4 -embedded OFET device, which led to greater ease in distinguishing the information storage levels. Moreover, the 1st (Sweep 1) and 2nd (Sweep 3) programming processes resulted in almost identical transfer curves upon applying negative pulses, which indicated that the programming/erasing cycle was suffi ciently repeatable to be categorized as a fl ash-type memory device.…”

“…[ 14 ] Here, the preparation of these nano fl oating gate structures with specifi c sizes, concentrations, and a controlled spatial distribution inside the dielectric layer is the key to achieve high device performance. Therefore, various techniques to prepare welldefi ned nano fl oating gates using thermal evaporation, [15][16][17][18] electrostatic assembly, [ 19,20 ] or block copolymer templates [21][22][23] have been demonstrated. Furthermore, not only metal nanoparticles but also nanocarbon materials or functional organic molecules, such as fullerenes, graphenes, or phthalocyanines, have been incorporated into the dielectric layer and have proved their applicability as nano fl oating gates.…”