Bias‐Stress‐Stable Low‐Voltage Organic Field‐Effect Transistors with Ultrathin Polymer Dielectric on C Nanoparticles

Abstract

both p-type and n-type OFETs. Based on the hybrid dielectrics, the operating gate bias ( V GS ) for the pentacene-based and N,N′ -ditridecyl-3,4,9,10-perylenetetracarboxylic diimide (PTCDI-C 13 H 27 )-based OFETs is down to −2 and 2 V, respectively. The devices exhibit typical µ FE , high ON/OFF ratio, and, in particular, excellent bias stress stability upon prolonged operation up to 6 × 10 4 s. The presence of the sputtered C NPs turns out to be the key for the formation of an ultrathin and pinhole-free polymer dielectric layer. This type of low-voltage OFETs with high operating stability can be realized on a fl exible substrate as well. Therefore, depositing an ultrathin low-k polymer on sputtered C NPs is a promising way for achieving high-performance low-voltage OFETs.The device structure of the low-voltage OFETs is schematically illustrated in Figure 1 , where a submonolayer of C is deposited by sputtering and spontaneously forms C NPs on Si. [ 23 ] The atomic force microscopy (AFM) image in Figure 1 demonstrates the uniform distribution of a number of C NPs on the substrate, and their height and lateral size are around 2 and 20 nm, respectively. The X-ray photoelectron spectroscopy (XPS) and Raman characterization results ( Figure S1, Supporting Information) suggest that the sputtered C NPs are amorphous C containing oxygenated groups and small graphite-like domains. [ 23 ] The C-NP-modifi ed Si surface possesses high surface energy and induces a small water contact angle of 45° (Figure 1 ), and the surface roughness is slightly increased from 0.17 ± 0.03 to 0.24 ± 0.03 nm upon the deposition of C NPs. Three kinds of low-k polymers, i.e., polystyrene (PS), polymethylmethacrylate (PMMA), and poly(2-vinyl naphthalene) (PVN), are then spin-coated onto the sputtered C NPs as the gate dielectrics (PS/C, PMMA/C, and PVN/C, respectively). The preparation conditions are controlled to deposit the dielectric layers as thin as 12-13 nm. Measured C i for the PS/C, PMMA/C, and PVN/C dielectrics ( Figure S2a,b, Supporting Information), about 180, 230, and 205 nF cm −2 , respectively, are quite large owing to their small d . Note that experimentally derived C i are well consistent with the theoretical ones calculated from k / d . For such ultrathin low-k dielectrics, the accumulated surface charge density ( n = C i V GS / q ) can be up to the order of 10 12 cm −2 at V GS = ±1 V, where q is the electron charge quantity. The pentacene/PTCDI-C 13 H 27 thin fi lm acts as the p-type/n-type organic active layer, respectively, and Cu on top is employed as the drain and source electrodes. [ 24 ] Figure 2 a-c shows the transfer characteristics of the pentacene-based low-voltage OFETs on the PS/C, PMMA/C, and PVN/C dielectrics, respectively, where the drain bias ( V DS ) is as low as −0.2 V and the V GS range is no higher than −2 V. I GS Organic fi eld-effect transistors (OFETs) are essential components in future fl exible, wearable, and portable electronic devices, which have numerous applications such as sensors, identifi cation ...

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