On-Wafer Characterization of Silicon Transistors Up To 500 GHz and Analysis of Measurement Discontinuities Between the Frequency Bands Sebastien Fregonese, Magali de Matos, Marina Deng, Manuel Potéreau, Cédric Ayela, Klaus Aufinger, Thomas Zimmer To cite this version: Sebastien Fregonese, Magali de Matos, Marina Deng, Manuel Potéreau, Cédric Ayela, et al.. On-Wafer Characterization of Silicon Transistors Up To 500 GHz and Analysis of Measurement Discontinuities Between the Frequency Bands. IEEE Transactions on Microwave Theory and Techniques, Institute of Electrical and Electronics Engineers, 2018, 66 (7), pp.3332-3341. 10.1109/TMTT.2018.2832067. hal-01818021 HAL Id: hal-01818021 https://hal.archives-ouvertes.fr/hal-01818021 Submitted on 27 Jun 2018 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. > REPLACE THIS LINE WITH YOUR PAPER IDENTIFICATION NUMBER (DOUBLE-CLICK HERE TO EDIT) < 1 On-wafer Characterization of Silicon Transistors up to 500 GHz And Analysis of Measurement Discontinuities between the Frequency Bands Sebastien Fregonese, Magali De Matos, Marina Deng, Manuel Potereau, Cedric Ayela, Klaus Aufinger and Thomas Zimmer as of the maximum available gain MAG. Calibration has been carried out with impedance standard substrate (ISS) and the Abstract— This paper investigates on-wafer characterization calibration methods used were LRRM (line-reflect-reflect- of SiGe HBTs up to 500 GHz. Test structures for on-wafer match) and TRL (Thru, Reflect, Line). In [14], Deng et al. have TRL calibration have been designed and are presented. The presented an exhaustive set of S parameter measurements up to TRL calibration method with silicon standards has first 325 GHz on HBTs from an advanced 55nm BiCMOS been benchmarked through EM-simulation. Passive and technology using a similar approach as [13] for calibration active components are then characterized up to 500 GHz. (LRRM on ISS ). Finally, Williams et al. [15] have presented The slight discontinuities between the frequency bands are measurement results from an silicon on insulator (SOI) explored. A specific focus was placed on incorrect technology, where passive elements have been characterized up horizontal probe positioning as well as on probe to 500 GHz, while the transistor measurement was performed deformation, resulting in a better assessment of possible up to 110 GHz. On-wafer TRL (and multiline-TRL) calibration measurement errors. was applied. Again Galatro et al. [16] have designed an on- wafer calibration-kit dedicated to transistor characterization. Index Terms—S parameter measurement, probe station, Measurement results are shown from 220 GHz up to 325 GHz. THz, SiGe HBT, on wafer, calibration, de-embedding The main issue related to off-wafer calibration with the ISS calibration-kit concerns discontinuities that are often observed I. INTRODUCTION from one frequency band to another frequency band. These UB-THZ system development based on very advanced discontinuities are attributed to spurious wave modes Ssilicon transistors and especially Silicon Germanium propagating into the substrate [7], to crosstalk [17] and to the bipolar-MOS (BiCMOS) technology opens new applications different measurement environments: calibration is performed for medical imaging, security and also automotive applications on ISS calibration-kit and the measurements are performed on like anti-collision radar [1]–[3]. The circuit design in this Si substrate. For example in [9] and [11], different calibrations frequency range is very challenging and requires accurate have been realized showing the limitations of calibrations on model cards for active and passive devices. To this aim, precise ISS compared to the on-wafer TRL. In [15], the TRL has been characterization and modelling of the devices in the sub-THz claimed as the calibration of reference for on-wafer frequency range is compulsory to optimize the circuit measurements at microwave frequencies. performance and to minimize the number of design to On the other hand, the difficulties related to on-Silicon wafer fabrication loops [4]. While very high frequency on-wafer calibration are: the less ideal characterization environment for measurement of III-V based devices and circuits have on-wafer measurement in terms of (i) substrate loss, (ii) back- frequently been published [5], [6], [7], [8], and reported up to end-of-line (BEOL) complexity and (iii) probe contact quality. 750 GHz [9], [10], the characterization of transistors above 110 For example, Williams et al. have reported the difficulty to GHz on Si-wafers remains challenging [11]. Only very few perform repeatable measurements on aluminum pads that are demonstrations of transistor measurements at higher commonly used in Silicon technologies [15] and the lower frequencies have been performed on silicon substrate [12]. quality of microstrip lines on SOI substrate compared to Voinigescu et al. [13] have demonstrated measurement up to microstrip lines using a benzocyclobutene (BCB) dielectric, 325 GHz of an advanced SiGe HBT (hetero-junction bipolar when measuring S parameters in the sub-THz frequency range. transistor) showing results of S21 and H21 parameters as well In addition, discontinuities on measured S parameters between This paragraph of the first footnote will contain the date on which you S. Fregonese, M. De Matos, M. Deng, M. Potereau, C. Ayela, And T. submitted your paper for review. Zimmer are with CNRS and Bordeaux Université, Bordeaux, France. (e-mail: This work is partly funded by the French Nouvelle-Aquitaine Authorities [email protected]). through the SUBTILE and FAST project. The authors also acknowledge Klaus Aufinger is with Infineon Technologies AG, 85579 Neubiberg, financial support from the EU under Project Taranto (No. 737454). Germany (e-mail: [email protected]). > REPLACE THIS LINE WITH YOUR PAPER IDENTIFICATION NUMBER (DOUBLE-CLICK HERE TO EDIT) < 2 the different frequency bands (1-110GHz, 220-325GHz, 325- A. Description Of Test Structures 500GHz) are often observed [18]. But very broad frequency The test structures have been designed in a 130 nm BiCMOS range measurements over the different frequency bands are technology from Infineon featuring 6 levels of Cu metals (see mandatory for device modelling, model accuracy and validity Fig. 1). The last level of Cu metal used for the design of the assessment. microstrip line is 2.8 µm thick. The ground plane is made The aim of this paper is (i) to present the design of an on-Si wafer stacking metal level 1 up to metal level 4 and the dielectric calibration-kit, (ii) to reveal a methodology to characterize thickness between ground plane and the line is about 4 µm. Pads passive devices and HBTs up to 500 GHz from a silicon have been designed for 50 µm probe pitch. The reference plane BiCMOS technology and (iii) to investigate the different is positioned after the pad and a piece of line of 4 µm (see Fig. origins for the frequency band discontinuities. 2). Concerning the TRL calibration, the through and the lines standards have a length of 50 µm, 160 µm and 560 µm, (see The remainder of this work is organized as follows. Section II Fig. 2 on the top left and in the middle). The 560µm line is used is dedicated to the analysis of the measurement results. To this for the measurement between 13 to 120 GHz, while the 160µm aim, the test structures are exhibited, the EM simulation-based long line is used from 70 GHz to 560 GHz. A pad-open was methodology is presented, and a thorough analysis of test used as the reflect. The pad-open is composed by the pad structure measurements is performed by comparison to EM including the 4 µm line only (see Fig 2 on the top right). Finally simulation using the same calibration technique. In Section III, a load was employed to extract the characteristic impedance measurement results are assessed versus simulation by using the methodology described in [21]. evaluating the variation in probe tip planarity, positioning, probe overdrive and the impact of probe deformation. Conclusions are then drawn in Section IV. II. CHARACTERIZATION RESULTS OF PASSIVE ELEMENTS AND SIGE HBT To cover the frequency range from 1 GHz to 500 GHz, four measurement benches were used: An E8361A Vector Network Analyzer (VNA) from Agilent working up to 110 GHz using frequency extenders (N5260-60003) above 67 GHz. Furthermore for the other frequency bands 220-330 GHz (WR- 3) and 325-500 GHz (WR-2), measurements were carried out with a four port Rohde & Schwarz ZVA24 VNA, coupled with Rohde & Schwarz VNA frequency extenders (ZC330 and ZC500, respectively). Despite the fact that we have the equipment to measure between 140 to 220 GHz, it was not possible to carry out the measurements. In fact, the geometry of the probe at port 2 is not compatible with the pad layout. The frequency extenders are installed on a SIGNATONE on-wafer probe station. The GSG probes used in this work are Picoprobe from GGB with a pitch of 50 µm in each frequency band. The signal power level is set to less than -32 dBm in the four bands for the measurement of active and passive elements. For all the frequency bands, raw on-wafer measurements have been carried out on dedicated test structures and the data have been processed by our in-house TRL calibration tool. A detailed description of the test structures is given in the following part. M7 Alu M6 Cu Two thick copper + one aluminium layer M5 Cu M4 Cu M3 Cu Four thin Fig.