My current research activity has three main orientations or lines:
1. Millimeter-wave Integrated Circuit Design in CPW technology,
The atmospheric windows at 140 and 220 GHz are of great interest for several applications like remote atmospheric sensing, aircraft landing, through-wall imaging, concealed weapon detection, or the next generation of automotive collision-avoidance radar. Submicron device scaling has made transistor-based electronics in the 140-220 GHz (G-band) range realizable. This research line currently focuses on the design, fabrication and experimental evaluation of MMICs in this frequency range. Concerning circuit functions, the main effort is placed on nonlinear circuits. This research work is carried out in cooperation with the Fraunhofer Institute for Applied Solid-State Physics in Freiburg, Germany (http://www.iaf.fraunhofer.de/), which is the leading institution in Europe for MMIC design and fabrication above 100 GHz. The MMICs (Monolithic Millimeter-wave Integrated Circuits) are based on the InAlAs/InGaAs metamorphic HEMT (MHEMT) processes available at the Fraunhofer IAF, in combination with coplanar waveguide technology (CPW).
Some chip photographs of the developed MMICs are shown in Figures 1-3. All of them show high performance (which is summarized in each figure caption). To the knowledge of the authors, the tripler is the first active one published at frequencies beyond 100 GHz.
Figure 1. 110-to-220 GHz MHEMT-based frequency doubler. The MMIC achieves a measured conversion gain of -7 dB for a 2.5-dBm input signal.The chip area is 1x1 mm2.
Figure 2. 46.6-to-140 MHEMT-based frequency tripler. The MMIC achieves a maximum measured conversion gain of -11 dB for an input power of 9 dBm. The chip size is 1x1.5 mm2.
Figure 3. D-band subharmonically-pumped resistive mixer. This MHEMT-based MMIC achieves a measured conversion loss between 12.5 and 16 dB in the RF frequency bandwidth from 120 to 150 GHz, with 4 dBm LO drive and an IF frequency of 100 MHz. The chip area is 1.2 x1.5 mm2.
Older activities, in relation to MMIC design, were focused on other frequency bands, HEMT processes and applications. To highlight are the activities in W-band (for automotive radar), based on the Fraunhofer IAF AlGaAs/InGaAs/GaAs 0.15 mm PHEMT process; V-band (for an application in the area of communications), with the same Fraunhofer IAF PHEMT process and with the former Alcatel-SEL as industry partner; and Ka-band (for Local Multipoint Distribution System), also with the Fraunhofer IAF and with Infineon-Technologies, Munich, as industry partner. In this latter case, Infineon PHEMT technology was used. Some of these research activities were funded by projects that are presented in the Project Section.
2. Transistor Modeling.
The design of millimeter-wave circuits requires accurate modelling tools, specially concerning the active device. The activity in this area has been focused both on small-signal and large-signal modelling.
The most recent result is the development of a new multibias approach for HEMT small-signal equivalent-circuit model extraction. The method is based on scaling rules and uses a hybrid direct extraction/particle swarm optimization-based approach. A single model for devices with different sizes is obtained. The extraction procedure has been successfully verified with measurements on PHEMTs and MHEMTs up to 70 and 120 GHz.
In relation to this research line, it is also to mention the experience in extraction of large-signal models.
3. Hybrid Microwave Integrated Circuits.
This line has started more recently and is carried out in cooperation with the Department of High Frequency Engineering (University of Kassel), led by Prof. Bangert (http://www.uni-kassel.de/fb16/hft/). There is a bilateral agreement between both universities that allows student exchange in the frame of LLP Erasmus programme. As a result of the cooperation, several bachelor’s thesis have recently been realized (see Supervision of Bachelor and Master's thesis in the Teaching Section). In the academic year 2012/13, the mobility agreement is extended to master’s students for the realization of master’s thesis in the field of passive circuits in microstrip technology and microwave transitions.