Imec, a nanoelectronics company, has demonstrated a high-speed SiGe:C heterojunction bipolar transistor (HBT) device designed for large volume millimeter-wave low-power circuits in applications for automotive radars.
Cross-section of bipolar HBT device in a B-E-B-C configuration after end-of-line processing
The HBT device has a fT of 245 GHz and fMAX of 450 GHz. These devices enable improved imaging systems for medical, scientific and security applications.
The SiGe:C HBT devices feature a self-aligned architecture and realize an effective collector doping profile. Their low-cost and high-density properties and ability to work with reduced power dissipation and very high frequencies make them apt for consumer applications. The high speed of the device allows it to be used for applications requiring a lower impact of temperature, voltage and process variations for increased circuit reliability at lower frequencies.
Collector dopants are inserted at the start of the process in thin sub-collector doping profiles for improving the performance of SiGe:C HBTs. The process flow’s thermal budget makes the correct positioning of the collector more difficult. Imec has introduced a less doped, well controlled, and thin collector region without increasing the complication of the process. This improves the performance of the HBT device and fMAX values over 450GHz are achieved. The scaling of the sub-collector doping profile does not affect the values of the collector-base capacitance. The emitter-base tunnel current is limited and the current gain averages around 400.