Stable organic static random access memory from a roll-to-roll compatible vacuum evaporation process

Journal article

An organic Static Random Access Memory (SRAM) based on p-type, six-transistor cells is demonstrated. The bottom-gate top-contact thin film transistors composing the memory were fabricated on flexible polyethylene naphthalate substrates. All metallization layers and the p-type semiconductor dinaphtho[2,3-b:2',3'-f] thieno[3,2-b]thiophene were deposited by thermal evaporation. The gate dielectric was deposited in a vacuum roll-to-roll environment at a web speed of 25 m/min by flash-evaporation and subsequent plasma polymerisation of tripropyleneglycol diacrylate (TPGDA). Buffering the TPGDA with a polystyrene layer yields hysteresis-free transistor characteristics with turn-on voltage close to zero. The static transfer characteristic of diode-connected load inverters were also hysteresis-free with maximum gain >2 and noise margin ∼2.5 V. When incorporated into SRAM cells the time-constant for writing data into individual SRAM cells was less than 0.4 ms. Little change occurred in the magnitude of the stored voltages, when the SRAM was powered continuously from a −40 V rail for over 27 h testifying to the electrical stability of the threshold voltage of the individual transistors. Unencapsulated SRAM cells measured two months after fabrication showed no significant degradation after storage in a clear plastic container in normal laboratory ambient.

Authors: Assender, H; Avila-Nino, J; Patchett, E; Taylor, D; Yeates, S

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Elsevier
• Journal: Organic Electronics
• Volume: 31
• Pages: 77-81
• Publication date: 2016-01-20
• DOI: 10.1016/j.orgel.2016.01.017
• ISSN: 1566-1199
• Keywords: thin film transistors; organic electronics; inverters; SRAM