Community Research and Development Information Service - CORDIS

Periodic Report Summary 1 - IN-POWER (InP DHBT MMIC Technology for Millimeter-Wave Power Applications)

The overall objective of the "IN-POWER" project is to develop an InP HBT technology optimized for millimeter-wave power applications. The development of the InP DHBT technology will be accompanied by the MMIC (Monolithic Microwave Integrated Circuit) implementation of PA's targeting emerging applications at E-band (71-76 and 81-86 GHz) and higher millimeter-wave frequencies. The project consists of an academic partner, the Technical University of Denmark, and an industrial partner, III-V Lab in France. Two ESRs have been recruited as part of the project.

The specific scientific and technological objectives of the “IN-POWER” project are the following:
• To optimize the circuit-oriented InP DHBT technology currently under development at the III-V Lab towards power applications at mm-wave frequencies. This involves an optimization of the vertical structure and geometry of the existing devices for high fmax, high breakdown voltage (>6 V), and extended safe-operating-area (SOA).
•To exploit commercially available software tools for thermal and electromagnetic (EM) simulation of power cell structures based on single- and multi-finger devices.
•To develop accurate electro-thermal large-signal models to aid the design of the mm-wave MMIC’s.
•To develop innovative design techniques for PA MMIC design at mm-wave frequencies. This includes techniques for effective on-chip power combination.

Single- and multi-finger devices of various geometries have been studied based on devices already available at III-V Lab from the beginning of the project. Optimization step consisting in a modification of the collector thickness for a reduced saturation region, larger breakdown voltage, and higher maximum frequency of oscillation have been performed. Characterization of devices from first fabrication run shows maximum frequency of oscillation of approximately 420 GHz for single-finger devices. This number presents a minor improvement compared to the results of 400 GHz obtained for the single-finger devices available at the beginning of the project. The breakdown voltage remains above 6 V after the device modifications. As expected the saturation region has been improved by the modification of the collector thickness. Devices with symmetrical and asymmetrical ballasting have also been fabricated. Improved ballasted device structures are presently being investigated in order to resolve an instability issue. For further optimization of the devices it has been decided to exploit Technology Computer Aided Design (TCAD) software due to the promise of increased physical insight. The expected final results should be transistors with fmax > 500 GHz and ballasted multi-finger devices with state-of-the-art performance at millimeter-wave frequencies.

On the circuit design side, the concept of device stacking for power amplifiers operating at E-band and higher millimeter-wave frequencies has been thoroughly investigated. By using a predictive electro-thermal large-signal model it has been shown that the stacked concept can be successfully applied up to frequencies around 140 GHz. A first fabrication of E-band power amplifiers using a two-device stacked configuration as the basic power cell has been taped-out. The E-band power amplifiers employs different combinations of single- and multi-finger devices with and without ballasting. Basically, the designed E-band power amplifiers can be classified into matched power cells, four-way combined power cells, and a four-way combined power cell with driver. Experimental results from the first fabrication run has been performed. The large-signal characterization shows a saturated output power of +10 dBm and +16.8 dBm at 84 GHz for the matched power cell using single-finger devices and four-finger devices, respectively. The output power of the four-way power combined E-band power amplifiers is more than 20 dBm in the lower E-band frequency range from 71-76 GHz. This is close to the values simulated using the predictive electro-thermal large-signal model and is indeed promising with respect to further exploitation of the InP DHBT technology for E-band power amplifiers. Present design effort using eigth-way power combining demonstrates around 26 dBm output power over a broadband bandwidth. These circuits is about to be taped-out. The study of power amplifiers for higher millimeter-wave frequencies has so far been limited. A concept to implement low-loss two-way power combining structures using elevated coplanar waveguides have been experimentally proven. The power combiners shows an insertion loss of around 0.5 dB at 140 GHz when tested on-wafer in a back-to-back configuration. The power combiner principle is currently exploited in the design of 140 GHz power amplifiers which are about to be taped-out.

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