N. Weimann

Flip-Chip Interconnects for 250 GHz Modules

With the increasing availability of MMICs at frequencies beyond 100 GHz low-loss interconnects for module fabrication in this frequency range become essential. This letter presents results on a flip-chip mounting approach exhibiting a bandwidth of more than 250 GHz, supporting both coplanar and stripline transitions. The interconnects are realized with 10 μm-diameter AuSn microbumps. S-parameter measurements show an insertion loss of less than 1.0 dB per interconnect and a return loss better than 10 dB up to 250 GHz. The experimental results are in good agreement with 3-D EM simulations.

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

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.

Multifinger Indium Phosphide Double-Heterostructure Transistor Circuit Technology With Integrated Diamond Heat Sink Layer

The RF power output of scaled subterahertz and terahertz indium phosphide double-heterostructure bipolar transistors (InP DHBTs) is limited by the thermal device resistance, which increases with the geometrical frequency scaling of these devices. We present a diamond thin-film heat sink process aimed at the efficient removal of the heat generated in submicrometer InP HBTs. The thin-film diamond is integrated in a wafer bond process. Vertical connections are facilitated by plasma-processed contact holes through the diamond layer, metallized with electroplated gold. The process is suitable for monolithic circuit integration, amenable to the realization of high-power analog circuits in the millimeter-wave region and beyond. The thermal resistance of double-finger transistors with a 0.8-μm emitter width could be reduced to 0.7 K/mW, while reaching the gain cutoff frequencies of fT = 360 GHz and fmax = 350 GHz. An integrated two-stage power amplifier with four-way power combining fabricated in this technology exhibited 20-dBm power output at 90 GHz with a bandwidth of 10 GHz.

A G-Band High Power Frequency Doubler in Transferred-Substrate InP HBT Technology

This letter presents a G-band balanced frequency doubler with high output power, realized using a 800 nm transferred-substrate InP-HBT process. The doubler delivers 5 dBm ±3 dBm in the range 140-220 GHz. The dc consumption is only 41 mW. To the knowledge of the authors, this is the highest output power for a wideband transistor based frequency doubler in the 140-220 GHz frequency range published so far. The results show the ability to implement a high output power G-band source in transferred-substrate InP HBT technology.

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

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 330 GHz hetero-integrated source in InP-on-BiCMOS technology

This paper presents a 330 GHz hetero-integrated signal source using InP-on-BiCMOS technology. It consists of a fundamental Voltage Controlled Oscillator (VCO) in 0.25 μm BiCMOS technology and a frequency quadrupler in 0.8 μm transferred substrate (TS) InP-HBT technology, which is integrated on top of the BiCMOS MMIC in a wafer-level BCB bonding process. The fundamental VCO operates at 82 GHz and the combined source delivers -12 dBm output power at 328 GHz. To the knowledge of the authors, this is the first hetero-integrated signal source in the frequency range beyond 300 GHz reported so far. It demonstrates the potential of the hetero-integration process for THz frequencies.

Performance study of a 248 GHz voltage controlled hetero-integrated source in InP-on-BiCMOS technology

This paper presents the performance study of a 248 GHz voltage-controlled hetero-integrated signal source using indium phosphide (InP)-on-bipolar complementary metal-oxide-semiconductor (BiCMOS) technology. The source consists of a voltage controlled oscillator (VCO) in 0.25 µm BiCMOS technology and a frequency multiplier in 0.8 µm transferred-substrate InP-heterojunction bipolar transistor technology, which is integrated on top of the BiCMOS monolithic microwave integrated circuit in a wafer-level based benzocyclobutene bonding process. The vertical transitions from BiCMOS to InP in this process exhibit broadband properties with insertion losses below 0.5 dB up to 325 GHz. The VCO operates at 82.7 GHz with an output power of 6 dBm and the combined circuit delivers −9 dBm at 248 GHz with 1.22% tuning range. The phase noise of the combined circuit is −85 dBc/Hz at 1 MHz offset. The measured output return loss of the hetero-integrated source is >10 dB within a broad frequency range. This result shows the potential of the hetero integrated process for THz frequencies.

A 330 GHz active frequency quadrupler in InP DHBT transferred-substrate technology

This paper presents a wideband 330 GHz frequency quadrupler using 0.8 μm transferred substrate (TS) InP-HBT technology. The process includes a heat-spreading diamond layer, which improves the power handling capability of the circuit. The quadrupler delivers -7 dBm output power at 325 GHz, at a DC consumption of only 40 mW, which corresponds to 0.5 % of efficiency. It achieves 90 GHz bandwidth and exhibits very low unwanted harmonics. The circuit utilizes a balanced architecture. The results demonstrate the potential of the InP TS.

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

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.

InP on BiCMOS technology platform for millimeter-wave and THz MMIC

This work presents a novel InP DHBT-SiGe BiCMOS technology platform by wafer-scale heterogeneous integration. The technology provides vertical stacking of processed InP DHBT wafers directly on top of processed BiCMOS wafer with low-loss ultrabroadband interconnects up to 200 GHz. We demonstrate first MMIC operating up to 300 GHz.