Title :
Influence of Mechanical Bending on Flexible InGaZnO-Based Ferroelectric Memory TFTs
Author :
Petti, L. ; Munzenrieder, N. ; Salvatore, G.A. ; Zysset, Christoph ; Kinkeldei, Thomas ; Buthe, L. ; Troster, G.
Author_Institution :
Inst. for Electron., Swiss Fed. Inst. of Technol. Zurich, Zurich, Switzerland
Abstract :
Future flexible electronic systems require memory devices combining low-power operation and mechanical bendability. Here, we present mechanically flexible amorphous InGaZnO (a-IGZO) memory thin-film transistors (TFTs) with a ferroelectric poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] gate insulator. Memory operation is demonstrated with a memory window of 3.2 V and a memory ON/OFF ratio of 1.5×106 (gate-source voltage sweep of ±6 V). The measured mobility of 8 cm2 V-1s-1 and the ON/OFF current ratio of 107 are comparable with the values for reference TFTs fabricated on the same substrate. To use memory TFTs in flexible applications, it is crucial to understand their behavior under mechanical strain. Flexible memory and reference TFTs are characterized under bending radii down to 5.5 mm, corresponding to tensile and compressive strain of ≈ ±0.6%. For both memory and reference TFTs, tensile strain causes negative threshold voltage shifts and increased drain currents, whereas compressive strain results in the opposite effects. However, memory TFTs, compared with reference TFTs, exhibit up to 8× larger threshold voltage shifts and 17× larger drain current variations. It is shown that the strain-dependent properties of a-IGZO can only explain the shifts observed in reference TFTs, whereas the variations in memory TFTs are mainly caused by the piezoelectric properties of P(VDF-TrFE).
Keywords :
bending; ferroelectric storage; flexible electronics; gallium compounds; indium compounds; thin film transistors; wide band gap semiconductors; InGaZnO; ON-OFF current ratio; P(VDF-TrFE) gate insulator; compressive strain; drain current variation; ferroelectric poly(vinylidene fluoride-trifluoroethylene) gate insulator; flexible electronic systems; flexible ferroelectric memory TFT; gate-source voltage sweep; increased drain current; low-power operation; mechanical bendability; mechanical bending; mechanical strain; mechanically flexible amorphous memory thin-film transistors; memory ON-OFF ratio; memory devices; memory operation; memory window; negative threshold voltage shift; piezoelectric properties; reference TFT value; strain-dependent properties; tensile strain; voltage 3.2 V; Aluminum oxide; Current measurement; Logic gates; Strain; Substrates; Thin film transistors; Threshold voltage; Ferroelectric poly(vinylidene fluoride-trifluoroethylene) P(VDF-TrFE); flexible electronics; indium-gallium-zinc oxide (IGZO); mechanical strain; thin-film transistor (TFT);
Journal_Title :
Electron Devices, IEEE Transactions on
DOI :
10.1109/TED.2014.2304307