Electronics devices based on graphene and carbon nanotubes (CNTs) have attracted significant attentions for potential radiofrequency (RF) applications [1-4]. It is shown that intrinsic current-gain and power-gain cutoff frequencies above 1 THz should be possible, but experimental demonstration using field-effect transistors (FETs) based on individual CNTs suffered from excessive parasitic effects and impedance mismatch problems. In order to overcome these limitations, great efforts have been concentrated on FETs made from aligned arrays of CNTs. Since all of the published CNT RF circuits were designed to work at linear region, it is often stated that it is necessary to use dense arrays of all-semiconducting nanotubes to achieve high performance. While impressive progress has been made in achieving high density arrays of CNTs, for example in several cases the required density of tens of nanotubes per μm has been realized, it is still challenging to eliminate all metallic CNTs without damaging semiconducting CNTs and thus severely degrading the performance of the CNT array FETs. Therefore most of the published RF integrated circuits based on CNT array on quartz only can operated at a relative low frequency far below 1 GHz owing to the low cut-off frequency of FETs. Here we argue that rather than trying to avoid the requirement of pure semiconducting CNTs, we may indeed make a good use of the natural growing CNTs for RF applications. We demonstrate that perfect ambipolar modulation may be achieved using FETs based on as-grown CNTs arrays on quartz near the minimum current point (MCP). Using the ambipolar region rather than linear region of these FETs, RF circuits including frequency multipliers and mixers are batch-fabricated and shown to outperform all previously reported carbon based RF circuits .
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