MMIC's characterization by very near‐field technique

Abstract

This paper shows a method to characterize microwave circuits using a near-field scanning microscope. Applied on various samples, it shows good resolution and weak disturbance for ICs operating with very common microwave components. Here, it is applied in an industrial INTRODUCTIONToday, in order to increase the MMIC bandwidth, it is necessary to decrease the scale factor down to the micrometer range. Consequently, the characterization of these devices becomes increasingly difficult or impossible. Due to the complexity of the circuit layout, electromagnetic simulators are unusable or ineffective. Some solutions have been proposed: Black et al. [1] built up a radiofrequency bench with a S.QU.I.D. that maps the magnetic field above a sample surface up to a few GHz. Another electromagnetic near-field mapping setup based on an electro-optic probe was proposed by Yang et al. [2] for up to 20 GHz. Keilmann et al. [3] proposed a setup that works in transmission mode with coaxial probes, allowing high-subwavelength resolution to be reached. Other works have been reported in [4 -8], where resonant coaxial line or waveguide was used to determine electromagnetic properties such as dielectric function, near-field polarimetry, or resistivity. Budka et al.[9] presented a modulated perturbation technique, which is an indirect method to map the electromagnetic field: the device under test (D.U.T.) is disturbed by a low-frequency modulated signal in its near-field range. In the work of Y. Gao and I. Wolff [10,11], a collection-scanning setup is proposed to diagnose high-frequencies circuits. These methods are either expensive (electro-optic sampling method), restrictive (low-temperature operation when using the S.QU.I.D., not broadband for resonnant cavities or waveguides, and map-only passive devices), or have a more complex setup (modulated perturbation method, use of a Vector Network Analyzer).In this paper, we present a collection method and a setup to map the electromagnetic near-field of active or passive microwave circuits by miniature coaxial cable, similar to Gao et al., but with no need of a Vector Network Analyzer (VNA) This setup also allows the mapping of the electromagnetic field near a self-emitting sample. It is a relatively simple setup, since it uses only common HF components (such as amplifiers and quadratic detectors). It is also a nondestructive method, as it works without contact to measure the different electromagnetic-field components based on the antennas's shape. The D.U.T. can be as complex as possible; the setup simply collects the electromagnetic near-field above its surface. The resolution reached is about 10 micrometers and the frequency range is from 0.01 to 20 GHz (limited by the amplifiers bandwidth). This paper also presents evaluations of the probe disturbance in the near-field zone for running ICs and industrial applications with this setup. EXPERIMENTAL SETUPThe D.U.T. is placed on a micrometric displacement table driven by a computer (see Fig. 1). This configuration enables us t...

Evanescent Waves Nuclear Magnetic Resonance

“…The Evanescent Wave probe is realized from a 50 Ω coaxial cable made from non magnetic copper alloy [ 10 , 12 ]. The inner conductor is 127 μm in diameter and the outer part is 584 μm , well below the NMR wavelength.…”