Resonator | EPFL Graph Search

A resonator is a device or system that exhibits resonance or resonant behavior. That is, it naturally oscillates with greater amplitude at some frequencies, called resonant frequencies, than at other frequencies. The oscillations in a resonator can be either electromagnetic or mechanical (including acoustic). Resonators are used to either generate waves of specific frequencies or to select specific frequencies from a signal. Musical instruments use acoustic resonators that produce sound waves of specific tones. Another example is quartz crystals used in electronic devices such as radio transmitters and quartz watches to produce oscillations of very precise frequency. A cavity resonator is one in which waves exist in a hollow space inside the device. In electronics and radio, microwave cavities consisting of hollow metal boxes are used in microwave transmitters, receivers and test equipment to control frequency, in place of the tuned circuits which are used at lower frequencies.

A low-power 2.4 GHz CMOS receiver using BAW resonators

Jérémie Chabloz

It has already been a few years since the first appearance of micro-electromechanical systems (MEMS) in academic research. Since then, a broad number of devices have been designed under this generic term. Bulk-acoustic wave (BAW) resonators are among the few of them which have become exploited at industrial level. They are mainly used to implement filters for mainstream telecommunication applications. In a different domain, potential applications for integrated wireless transceivers are flourishing. While some of them require always higher data rates, others need devices with low data rate but even lower power consumption. The goal of this thesis is to explore ways of using BAW resonators to implement building blocks for such a low-power radio and actually verify the postulate that this could help improving power consumption as well as miniaturize key functionalities. For the active integrated circuit part, the choice of a standard digital 0.18µm CMOS process established itself for its low cost and ubiquity. The specifications for the developed radio receiver are calculated for a physical layer derived from the well known Bluetooth communication protocol in the 2.4GHz ISM band with similar applications scenarii but with much lower data rates and wider channel spacing. After presenting the advantages and limitations of the devices, the implications for using BAWresonators to implement a low-power radio are investigated at circuit and system levels and a super-heterodyne architecture is proposed. A selective low-noise amplifier (LNA) is used at the circuit front-end to yield image and blocker rejection. Measurements for the RF front-end comprising an external balun, the selective LNA, a first downconversionmixer and an intermediate-frequency (IF) amplifier showed an overall noise figure of 11dB for a current consumption of 1.5mA under 1.2V. The high selectivity of the design yields an image rejection ratio of at least 50dB and allows to decrease linearity requirements and thus power consumption. A slightly improved version of the same front-end integrated together with the analog baseband signal processing chain but still using external local oscillators showed sensitivities of -96dBm at 100kbps symbol rate and -93dBm at 200kbps with an external state-of-the art FSK demodulator, allowing to extrapolate a global noise figure of 12.2dB for a global current consumption of 2.3mA under 1.2V. The proposed solution for the frequency synthesis uses both a BAW oscillator for the first downconversion to IF and a quadrature quasi-harmonic relaxation oscillator to translate the signals to baseband. The relaxation oscillator is embedded within a phase-locked loop (PLL) for which all the required blocks are discussed. Particularly, a novel modular multi-modulus frequency divider is presented, which does not necessitate complicated logic to yield the wanted division ratio and uses dynamic logic. The necessary digital circuitry to control the frequency generation is discussed as well. Finally, measurements for the complete receiver using the proposed frequency synthesis as well as digital control and demodulator implemented on FPGA are presented.

EPFL2008

Inflight Microwave Drying Process of Micro-droplets for High Resolution 3D printing

Kwanghoon Choi

A new Additive-Manufacturing (AM) or 3D printing concept is proposed to improve the printing resolution for metal additive manufacturing in the frame of the SFA-AM project, Powder Focusing for Beam-Induced Laser 3D Printing. The project aims to transport small powder particles (largest diameter < 10 um) at a high throughput to a spot smaller than 20 µm. To realize the objective, a metal ion included liquid is suggested as a source medium similar to the inkjet process, and the droplet is employed as a container for the metal ion transport. The key challenges of achieving this goal are 1) droplet size control and 2) efficient microwave heating that can dry the liquid portion of the dynamic droplet at a high-speed (3 m/s). The most demanding part is the development of a miniaturized, very concentrated field density microwave resonator where the droplet is passing through. This follows from the extremely short interaction time between the microwave and the ejected droplets (research: 0.5 ms) which results from the requirement for a small system size for its integration. The primary medium examined for the experiment is water due to 1) a high dielectric loss proportional to the drying efficiency and 2) avoiding explosion risks at the laser sintering stage compared to organic solutions. Various droplet generation conditions were investigated to determine the optimum conditions for the custom droplet generator, in particular, two key parameters were focused on: frequency and flow rate. The droplets obtained were analyzed with respect to size, gap distance, and linearity affecting the uniformity of the AM process. Moreover, Navier-Stokes-based fluid dynamics simulations enabled understanding of droplets behaviors, especially break-up formation. Eventually, the optimal condition for producing the smallest droplets with a diameter of 100 µm is determined to be 15 kHz and 0.5 ml/min. Such droplets loaded with metallic particles could result in smaller than 20 um of remaining metal powders aggregate after the drying process.A new TEM (Transverse ElectroMagnetic) resonator has been developed for drying and sensing applications. A full-wave electromagnetic simulation software, CST Microwave Studio, supported the working mode of the device. Firstly, it is used for the dielectric characterizations of different water-ethanol mixtures contained in a micro capillary. The sensing relies on electric field perturbation due to the inserted sample, and is measured based on the change of both resonance frequency and Q-factor. These sample-dependent variations were analyzed to estimate the complex permittivity using different methods such as the Perturbation Method (PM), Least-Square Model (LSM), and Log-Linear Model (LLM). This work demonstrates that the proposed microwave module is capable of sensing nano-liter volume ranges even though the samples only partially influence the sensing area (error < 13 % in permittivity). In microwave heating, the developed resonator achieved a temperature increase of 28 K in the microwave exposal time of 0.5 ms when the microwave power of 45 W was applied. Finally, numerical models have been proposed to estimate the maximum temperature of the initial droplet before cooling starts attributable to heat and mass transfer. This model well corresponds to the microwave electromagnetic simulation resulting in similar temperature deviations. It helps to determine the net heating efficiency of the microwave device.

EPFL2022

Micromachined tunable devices based on silicon integrated BaxSr1-xTiO3 thin films

Andreas Nöth

Thin Film Bulk Acoustic Wave Resonators (TFBARs) had been developed a decade ago and since then were implemented extensively in mobile communications devices. The "heart" of a TFBAR consists of a piezoelectric film that operates as an acousto-electric transducer, stabilizing the transmission at a given predetermined frequency. For reasons such as space economy in hand-held devices, it is of interest to make these TFBARs tunable, so that a single TFBAR is multi-band responsive. This thesis demonstrates for the first time electrically tunable, single-component TFBARs. A theory describing the tuning behavior of dc bias induced acoustic resonances was developed. Then we made the hypothesis that dc bias induced piezoelectric BaxSr1-xTiO3 (BST) thin films – namely, paraelectric, non-piezoelectric films operating under dc bias – can be used to make electrically tunable TFBARs and that the devices can be switched on or off depending on the dc bias state. The devices were then fabricated: We integrated BST lms onto silicon substrates, micromachined the substrate to create the TFBARs and a new type of suspended planar capacitor which were then characterized, analyzed, and modeled, demonstrating successfully the new concept: We developed a theory describing the electrical tuning behavior of the dc bias induced acoustic resonances in paraelectric thin lms in terms of material parameters. The field dependent constitutive piezoelectric equations were derived from the Landau free energy P-expansion by taking the linear and nonlinear electrostrictive terms as well as the background permittivity into account. We considered two modes of excitation for the tuning of the acoustic resonances, namely the thickness excitation (TE) mode and the lateral field excitation (LFE) mode. The tuning behavior of the two types of resonators based on BST thin films was modeled and discussed. For the modeling we calculated the relevant tensor components controlling the tuning of the BST resonators from the available literature data. The fabrication of the membrane-type TFBARs was realized by integrating BST thin films onto silicon substrates and using micromaching technologies. We showed that the developed TFBARs can be switched on or off with a dc bias. At a dc electric field of 615 kV/cm we observed a tuning of -2.4% (-66 MHz) and -0.6% (-16 MHz) for the resonance and antiresonance frequencies of the device, while the resonance frequency at a dc electric field extrapolated to 0 kV/cm was 2.85 GHz. The effective electromechanical coupling factor k2eff of the device increased up to 4.4%. The tuning was non-hysteretic. The Quality-factor (Q-factor) of the device was about 200. The developed micromaching processes for the TFBARs were used to fabricate coplanar BST capacitors on silicon. Micromaching was used to remove the Si substrate under the active area of the device. Comparing this new micromachined coplanar capacitor with conventional non-micromachined capacitors, we demonstrated that the removal of the substrate from the active device area resulted in a reduction of parasitic effects. The micromachined coplanar capacitor showed an increased tunability and a reduced loss tangent in comparison to the non-micromachined capacitor. The micromachined capacitor showed a relative tunability of 37% at a dc electric field of 1100 kV/cm. The loss tangent was 0.08 and 0.06 at zero and maximum dc bias, respectively, at a measurement frequency of 20 GHz. The integration of epitaxial BST thin films on silicon was studied as well because of its potential improvement of the device performance in comparison to devices based on polycrystalline films. Two different electrode/buffer layer systems, YBa2Cu3O7-x (YBCO) / CeO2 / YxZr1-xO2-x/2 (YSZ) and TiN were used for the integration. Epitaxial BST thin films were grown with both structures. For the BST / YBCO / CeO2 / YSZ / Si structure, the BST unit cell was rotated by 45° in the in-plane dimension with respect to the substrate. The BST layer exhibited good structural quality as indicated by a Full Width at Half Maximum (FWHM) of 0.5° of the rocking curve of the BST(002) diffraction peak. For the BST / TiN / Si structure, the BST layer was grown with a cube-on-cube epitaxial relationship on the silicon substrate, thus demonstrating epitaxially grown BST on silicon using conventional bottom electrode that is easily acceptable by the microelectronic industry. However, in this case, the structural quality of the BST layer was reduced in comparison to the BST / YBCO / CeO2 / YSZ / Si structure. The FWHM of the rocking curve of the BST(002) diffraction peak was 2.2°. We established the temperature (T=550 to 600 °C) and pressure (p ≈ 10-7 to 5 × 10-4 Torr) conditions for the growth of epitaxial BST thin films on TiN-buffered Si. At too high temperatures and/or oxygen pressures epitaxial BST thin film growth was impeded due to the oxidation of the TiN layer. By introducing experimental results from the electrical characterization of the micromachined devices with the polycrystalline BST into our developed theory, we could successfully model the tuning behavior of our fabricated TFBARs. The modeling allowed us to de-embed the intrinsic electromechanical properties of a freestanding BST layer. The effect of increasing mechanical load on the tuning performance of the device was modeled and studied experimentally. Under strong mechanical load, the tuning of both resonance and antiresonance frequency was reduced. The effect was attributed to a reduction in the tuning of k2eff of the device and of the sound velocity of the BST layer.

EPFL2009