Wafer-scale graphene/ferroelectric hybrid devices for low-voltage electronics

Abstract

Preparing graphene and its derivatives on functional substrates may open enormous opportunities for exploring the intrinsic electronic properties and new functionalities of graphene. However, efforts in replacing SiO2 have been greatly hampered by a very low sample yield of the exfoliation and related transferring methods. Here, we report a new route in exploring new graphene physics and functionalities by transferring large-scale chemical vapor deposition single-layer and bilayer graphene to functional substrates. Using ferroelectric Pb(Zr0.3Ti0.7)O3 (PZT), we demonstrate ultra-low voltage operation of graphene field effect transistors within ±1 V with maximum doping exceeding 10 13 cm −2 and on-off ratios larger than 10 times. After polarizing PZT, switching of graphene field effect transistors are characterized by pronounced resistance hysteresis, suitable for ultra-fast non-volatile electronics.PACS numbers: 72.80.VpAs a one-atom-thick single crystal, graphene's electronic properties [1] are closely related to its supporting substrates. SiO 2 provides excellent optical contrast, the key in discovering graphene by micromechanical exfoliation, but with critical drawbacks, such as surface roughness, high concentration of surface impurity charges, surface optical phonons, hydrophilic surface properties, and low dielectric constant (κ SiO2 = 3.9). Such drawbacks not only limit the carrier mobility but also the dielectric gating strength by the maximum polarizability P max = ε 0 κ SiO2 E max ≈ 1.7 µC/cm 2 , where E max ≈ 0.5 V /nm is the breakdown field of SiO 2 . Substantial progresses in replacing SiO 2 have already been made, such as significant mobility enhancement of single-layer graphene on boron nitride [2], and non-volatile polymer (top) gating of single-layer graphene [3,4]. However, efforts in this direction are in general constrained by the difficulty of exfoliating and identifying in particular single and bilayer graphene on different substrates.The rapid progresses in Copper-based chemical vapor deposition methods (Cu-CVD) have now made waferscale graphene synthesis and graphene transfer feasible both for single-layer graphene (SLG) [2, 5] and bilayer graphene (BLG) [6], providing great advantages in substrate engineering of graphene for exploring new physics and functionalities [3,[7][8][9][10][11]. With respect to substrates, ferroelectric materials are unique both in non-volatile gating [3] and high polarizability up to 100 µC/cm 2 (6 × 10 14 cm −2 in charge density) [12], 60 times larger than SiO 2 . With such high gating strength, it is possible to heavily dope graphene beyond the linear band dispersion regime (∼ 1 eV) and reach the van Hove singularities [13]. Such high doping, which in contrast to electrolyte gating [14] is gate-tunable even at liquid helium temperature, may also be of great importance for verifying the recent theoretical prediction of strong electron-phonon interactions and high-temperature superconductivity in graphane and related materials [15]. For graphene electronics, this...

Extrinsic and Intrinsic Charge Trapping at the Graphene/Ferroelectric Interface

“…In comparison, for the devices with graphene deposited at ambient temperature, the characteristics are similar to what was previously reported on CVD graphene on PZT substrates 5 : the anti-hysteresis behavior persists for all the gate voltage ramping ranges, with electron and hole trapping being roughly symmetric (Supporting Information Figure S3). This is demonstrated by significant shifts of both the forward and backward ramped Dirac peaks, with V BG range, for such samples.…”

“…Further studies focused on combining graphene with high quality single crystal thin films, allowing atomically flat surface, large gate capacitance, and low switching voltage operations. In those devices however, an inverse resistance hysteresis (antihysteresis) of the graphene channel was typically observed 4,5,8 . The robust nature of this antihysteresis was attributed to water molecules 8 and large densities of H + and OH -ions 9 , which screen the polarization between the graphene/PZT interface.…”

Modulation of mid-IR radiation by a gated graphene on ferroelectric substrate

“…Graphene placed on such the substrates has been intensively studied in the recent years (see, e.g., [5][6][7]). An unusual hysteresis in the resistance has been found to occur in the gate sweeps at high voltages, due to ferroelectric properties of the substrates.…”

Tunnel and electrostatic coupling in graphene-LaAlO3/SrTiO3 hybrid systems

“…A very efficient reciprocal gating of the two neighboring 2-dimensional systems is shown. A pronounced rectifying behavior is observed for larger bias values and ascribed to the interplay between electrostatic field-effects and tunneling across the LaAlO 3 barrier. The relevance of these results in the context of strongly coupled bilayer systems is discussed.…”

“…In particular, interaction with the host substrate offers new ways to tune the properties of graphene and the case of functional transition metal oxides is of significant interest. For instance, graphene field-effect transistors (FETs) built on ferroelectric Pb(Zr, Ti)O 3 substrates display pronounced memory effects, ultra-low voltage operation, 3 and open the way to novel nanoplasmonic devices. 4 Similarly, graphene photo-sensitivity was shown to increase 25 times on TiO 2 substrates 5 and intriguing magnetic phenomena are actively pursued in devices combining graphene with EuO substrates 6 or magnetic La x Sr 1−x MnO 3 electrodes.…”