Graphene audio voltage amplifier.

The main building block of analogue electronics is a voltage amplifier: an electronic device capable of amplifying small alternating current (AC) voltage signals. Many graphene[1] analogue electronic devices performing different functions[2–7] have recently been proposed, stemming from high carrier mobility[8–10] and ambipolar transport in graphene fieldeffect transistors (FETs). However, none of these devices was capable of signal amplification, thus ultimately requiring integration with Si transistors for performing this most important task. Here, we demonstrate an integrated graphene voltage amplifier which, together with the recently reported highfrequency graphene voltage amplifier,[11] paves the way for all-graphene analogue electronics. Signal amplification was obtained by fabricating graphene transistors in which the top gate overlaps with the source and drain contacts. This results in full-channel gating and therefore high transconductance at room temperature. The fabricated complementary push–pull amplifier has a voltage gain of 3.7 (11.4 dB) at 10 kHz, a total harmonic distortion in the audio frequency range of <1%, a unity-gain frequency of 360 kHz and a −3 dB bandwidth of 70 kHz (tested limits). The obtained values demonstrate that, among other applications, the present graphene amplifier is suitable for high fidelity amplification of audio signals. Graphene is emerging as a possible replacement for Si in future nanoelectronic devices. The high mobility of charge carriers in graphene[8–10] allows fabrication of very fast transistors,[12–15] having a potential to overcome state-of-the-art Si and III–V semiconductor-based high-frequency FETs at the ultimate scaling limits.[16] In contrast to Si, carrier transport in graphene is ambipolar, and this allows the same functionalities—such as logic gates,[17] frequency doublers,[2] analogue mixers,[3] and phase modulators[4] and detectors[6,7]—to be