Showing papers by "Nils Weimann published in 2014"

On-wafer small-signal and large-signal measurements up to sub-THz frequencies

Abstract: Recent advances in MMIC technology have opened the possibilities for circuit operation in the THz range. There are numerous examples of BiCMOS and III-V compound device technologies with demonstrated performance beyond 600 GHz. Characterization of such MMIC are predominantly performed on-wafer in a planar environment. However, on-wafer characterization facilities do not fully keep pace with MMIC development in terms of frequency and power. The paper discusses issues involved in on-wafer calibration at mm-wave frequencies, which is the basis for accurate measurements and characterization of active and passive device. Subsequently, the paper discusses mm-wave interconnect characterization. Low-loss interconnects are important for mm-wave MMIC, especially in case of heterogeneous integration. Finally, a novel heterogeneous integration approach of bipolar technologies, using both BiCMOS and InP DHBT processes is presented. This approach heavily relies on low-loss interconnects and accurate device modelling. It will be shown that accurate large-signal models can be efficiently extracted from well-calibrated on-wafer multi-bias small-signal measurements, but verification is difficult due to calibration difficulties at mm-wave frequencies.

(Invited) Combining SiGe BiCMOS and InP Processing in an on-top of Chip Integration Approach

Abstract: Applications such as radar imaging and wideband communications are driving the research on millimeter-wave circuits. For some applications SiGe hetero junction bipolar transistors (HBTs) are limited in output power. III-V technologies (like InP) can realize devices showing a high product of peak transit frequency multiplied with the open base breakdown voltage. Therefore, merging the qualities of both III-V and Si technology will enable a new class of high-performance ICs. Our approach combines an InP-DHBT transferred-substrate process with a Si-BiCMOS process. The key method is an aligned face-to-face wafer bonding with a subsequent removal of the InP substrate. Different integrated signal sources with an output frequency up to 246 GHz were designed and produced using different combinations of BiCMOS and InP circuit building blocks to demonstrate the capabilities of the hetero-integration routine. In this paper the influences of the wafer bonding and the finalization of the InP-DHBT process on SiGe devices were investigated. It was found that the influences on the BiCMOS devices were rather small.

Small- and large-signal modeling of InP HBTs in transferred-substrate technology

Abstract: In this paper, the small- and large-signal modeling of InP heterojunction bipolar transistors (HBTs) in transferred substrate (TS) technology is investigated. The small-signal equivalent circuit parameters for TS-HBTs in two-terminal and three-terminal configurations are determined by employing a direct parameter extraction methodology dedicated to III–V based HBTs. It is shown that the modeling of measured S-parameters can be improved in the millimeter-wave frequency range by augmenting the small-signal model with a description of AC current crowding. The extracted elements of the small-signal model structure are employed as a starting point for the extraction of a large-signal model. The developed large-signal model for the TS-HBTs accurately predicts the DC over temperature and small-signal performance over bias as well as the large-signal performance at millimeter-wave frequencies.

Silicon nitride stop layer in back-end-of-line planarization for wafer bonding application

Abstract: We introduce an approach that combines a 3” InP-DHBT transferred-substrate process with a SiGe-BiCMOS process. First, silicon and InP wafers are processed separately in different fabs. The silicon wafer runs through the complete 0.25 μm BiCMOS production process with five metal layers aluminum/tungsten back-end-of-line using silicon dioxide as dielectric. The processing was adapted for the following wafer bond process by planarization of the topmost metal level. This process flow was improved by using a SiN CMP stop layer on top of the metal layer stack, comparable to trench fill planarization. In that way a low surface topography was reached, this guarantees proper bonding results. Different mm-wave circuits operating at frequencies up to 246 GHz were produced to demonstrate the capability of the process flow.

A 270 GHz push-push oscillator in InP-DHBT-on-BiCMOS technology

Abstract: A 270-GHz reflection-type push-push oscillator is presented, realized using 0.8μm emitter InP-DHBTs. The InP DHBT-on-BiCMOS offers both InP HBT and BiCMOS technologies but in this case only the InP part is used. The transistors exhibit a maximum oscillation frequency fmax of 300 GHz. The oscillator delivers -9.5 dBm output power. DC consumption is only 31 mW from a 1.8 volts power supply, which corresponds to 0.4 % overall DC-to-RF efficiency.