Carbon Nanotubes Directly Integrated in CMOS by Local Synthesis - Towards a Wafer-Level Process

Integrating nanomaterials in electronic circuitry and in microsystems is highly desired for fully exploiting the functionality of nanomaterials such as Carbon Nanotubes (CNTs), utilizing the signal processing of micro/nano-electronics such as CMOS. An example device is a CNT-based gas sensor, where the extreme surface-to-volume ratio of CNTs provides ultra-high sensitivity, and direct integration with CMOS enables a device rendering processed, amplified and calibrated signals in a single, low-cost device. The CNTs should be synthesized on-chip directly into electric circuits. One challenge to overcome is the contradiction between temperature requirements for CNT growth (800-1000 °C) and CMOS compatibility (<; 300°C). We can achieve local CNT growth temperatures while keeping the main part of the chip at CMOS compatible temperatures by designing resistive micro-heaters. Synthesized CNTs are directed towards an electrode for desired contact by applying a voltage that gives a guiding electric field. All process parameters are controlled electrically, enabling a wafer-level process compatible with high-volume, low-cost manufacturing. This paper shows results from CNT integration in test vehicles manufactured in MEMS processes (using silicon microheaters), as well as our status towards realizing CNT integration in a purpose-designed CMOS chip (optionally using the chip's metal or polysilicon layers for microheaters).