Magali De Matos

Source-Pull and Load-Pull Characterization of Graphene FET

This paper presents the characterization of a GFET transistor using a source-pull/load-pull test set. The characterization shows that despite the good fT and fMAX, it is hard to achieve power gain using the GFET device within a circuit configuration. This is due to the very high impedance at the gate making impedance matching at the input extremely difficult. S-parameter characterization is performed and the associated small signal model is developed in order to further analyse and extrapolate the source-pull and load-pull measurement results. A good agreement is observed between small signal model simulation results and source-pull/load-pull measurements. Finally, the model is used to evaluate the optimum power gain of the transistor in a circuit configuration under matched conditions.

Substrate-coupling effect in BiCMOS technology for millimeter wave applications

This paper presents a detailed analysis of substrate coupling effects. Two types of coupling are considered. (i) Coupling from the device to the substrate and (ii) coupling between two neighboring devices. To assess the substrate coupling effect, specific test-structures have been designed for the mmW characterization. Various devices dimensions and distance between two neighboring devices have been fabricated for investigation. In addition, the associated deembedding structures have also been added on the test-structure such as the open, short, open and open-pad structures. Finally, S parameters measurements are performed up to 110 GHz and the substrate-coupling is investigated. To validate the analysis, Sentaurus TCAD simulations are used. A comparison between the S-parameters measurements and TCAD results is given. Finally, a scalable compact model based on lumped elements is proposed for the circuit design in the sub-THz range.

Graphene FET evaluation for RF and mmWave circuit applications

This letter presents the characterisation of a GFET transistor with a source-pull/load-pull test bench. The characterisation shows that despite the good fT and fMAX, it is hard to achieve reasonable power gain using the GFET device in a circuit configuration. This is due to the very high impedance at the gate making impedance matching at the input extremely difficult. An electrical model is used to evaluate the optimum power gain of the transistor under matched conditions. In a second part, a benchmarking of the technology is realized through accurate simulation of an optimised GFET device. Based on this input data, a compact model permits the evaluation of the GFET for high frequency amplifications.

On-Wafer Characterization of Silicon Transistors Up To 500 GHz and Analysis of Measurement Discontinuities Between the Frequency Bands

This paper investigates on-wafer characterization of SiGe HBTs up to 500 GHz. Test structures for on-wafer thru-reflect-line (TRL) calibration have been designed and are presented. The TRL calibration method with silicon standards has first been benchmarked through electromagnetic simulation. Passive and active components are then characterized up to 500 GHz. The slight discontinuities between the frequency bands are explored. A specific focus was placed on incorrect horizontal probe positioning as well as on probe deformation, resulting in a better assessment of possible measurement errors.

On the development of a novel high VSWR programmable impedance tuner

Impedance tuners are key instruments used for load- and source–pull measurements. They are crucial for any active microwave components, circuits, and systems characterization and optimization. This paper reports theoretical, simulated, and experimental results related to the development of a novel programmable impedance tuner offering high-voltage standing wave ratio (VSWR). After presenting the proposed tuner principle, a fabricated prototype operating at microwave frequencies and based on a 3.5 mm coaxial line is introduced with experimental results. Depending on the targeted frequency band, different pairs of slugs, with optimized length and characteristic impedance, can be used to obtain an optimal VSWR. This first prototype allowed us to demonstrate the interest of the proposed impedance synthesis principle and to identify ways forward to further improve its performances and push forward this promising technology.