(Invited) Multifunctional Technology with Monolithic Integrated THz-, Photonic- and µ-Fluidic Modules
Authors: Mai Andreas , Lischke Stefan , Wietstruck Matthias , Zimmermann Lars , Kaynak Mehmet , Tillack Bernd 
Published: February 2020

Beside the use of the continuously scaled silicon-based integrated-circuit technologies there is an increased demand of “More-than-Moore” (MtM) components, modules and technologies to serve the requirements of new applications e.g. in the communication market or in big data processing centers. The MtM approach describes the diversification of functionality on a reasonable scaling level and is according to the ITRS one of the key drivers for future communication products. The strategies to increase the functionality of an integrated circuit or system by the integration of MTM components can be distinguished to monolithic and heterogeneous integration concepts, respectively. The latter one enables in general a high flexibility for the combination of different functionalities as CMOS, MEMS (micro-electro-mechanical systems) or III-V devices. However, a reliable packaging and therefore a sufficient yield can be a major concern for these systems. The monolithic integration of modules and devices with advanced functionality in a baseline CMOS process can overcome this concern. However these integration concepts have to consider issues during the integration of different modules like the interaction of process steps to the performance of the devices.

In this paper we present a multifunctional technology platform with different monolithic integrated modules like THz devices, i.e. complementary SiGe heterojunction bipolar transistors, silicon photonics components as waveguides, photo detectors and modulators, and finally the wafer-level integration of µ-fluidic channels.

The continuous improvement of SiGe-BiCMOS technologies have proven their demand for instance in the automotive radar market. Mid- and long-range radar systems at 77 GHz can be realized by using HBTs with maximum oscillation frequencies (fmax) of 300 GHz. The power consumption of these systems can be significantly reduced by the use of available SiGe-BiCMOS technologies with fmax of 500 GHz. Addditional new applications as THz circuits for gas spectroscopy and chipsets for sensing and short-range wireless communication have been demonstrated with these technologies. In future novel systems as short-range-radar (SRR) or autonomous cruise control (ACC) at frequencies of 120 and 150GHz can be targeted by the use of next generation SiGe-BiCMOS technologies. According to the ITRS one main challenge of group-IV bipolar technologies is the determination of a reasonable “plateau technology” i.e. the best ratio of fT/fmax of the fast npn-HBTs as well as the realization of complementary devices. In this work we review the continuous progress of high-speed npn-HBTs and the realization of the fastest pnp-HBT with maximum oscillation frequencies of 265GHz in an IHP-BiCMOS process.

The demand for opto-electronic technologies in the market of big data processing centers increase continuously because of the necessity to handle the steadily growing data volumes. Recently we introduced the monolithic integration of photonic components as silicon-waveguides, high speed germanium-photo detectors and silicon based mach-zehnder-modulators (MZM) with high speed SiGe-BiCMOS devices in a joint technology. This new electro-photonic-integrated-circuit (EPIC) technology enables new applications as fully integrated linear 40Gbps receiver or SP-QPSK receiver for 28Gbaud operation. These circuits are among best in class and outperform monolithically Si integrated receivers fabricated elsewhere, e.g. with a Photonics-CMOS platform. However, there are several challenges during the monolithic integration of these photonic components in a SiGe-BiCMOS environment as the realization of a mixed substrate (SOI and bulk) or process optimizations to enable high-performance SiGe-HBTs and high speed Ge-photo detectors on the same wafer.

The last part of the paper describes the wafer level integration of micro-fluidic channels in a SiGe-BiCMOS technology. The silicon channels were realized by a deep silicon substrate etching from the wafer backside after the SiGe-BiCMOS process on the front side of the wafer is almost finished. The local backside etching (LBE) process requires specific conditions on the front side to enable a save and reliable process on the backside (chemical-mechanical-polishing (CMP), photo-lithography, reactive-ion etching (RIE)). The in- and outlet of the fluidic channels are realized on a separate silicon wafer by different deep RIE processes. Finally both wafers were bonded permanently. With this approach high frequency circuits which were realized in the SiGe-BiCMOS front- and back end can be used for sensor applications to investigate small volumes of fluids in the µ-channels for instance in bio-medical applications.

The paper reviews the monolithic integration of different modules and components to realize a multifunctional technology. We show challenges and benefits of this monolithic integration approach for the realization of a complex “More-than-Moore” technology.