This paper reviews the latest developments in microwave acoustic wave devices.After an introduction and brief history of bulk acoustic wave (BAW) and surface acoustic wave (SAW) devices, a review is given for guided SAWs and XBARs -two new technologies, which are promising for future 5G applications.Following this, we discuss recent simulation techniques, such as 3D finite element method (3D FEM) and simulation of nonlinearities, as well as filter synthesis.Next, a review on tunable and reconfigurable acoustics is given.Finally, we present the latest developments in microwave acoustics for millimeter-wave (mm-wave) operation as well as BAW oscillators.

Highly miniaturized wireless sensors will enable new healthcare sensing modalities such as ultra-small wearables, implantables, smart pills, etc. Bluetooth Low Energy (BLE) links to sensors improves user experience but necessitate a highly integrated, miniaturized BLE transmitter. Commercially available BLE transmitters are often unsuitable as they need a quartz crystal and multiple bulky external components, and are unable to operate from small silver oxide batteries which can have source impedances >40 Ω. While crystal-free transmitters have been published [1], they are either not standards compliant or remain research prototypes. In this paper, we present an FBAR-based (thin-Film Bulk Acoustic wave Resonator) [2] standards compliant BLE broadcaster module with an operating temperature range of 15C to +70C suitable for mass-produced volume-constrained sensors. All necessary electronics including the 65nm CMOS chip and FBAR frequency reference are integrated in a module with a volume of 1.53 mm3 (lowest reported to date).

The ability to achieve ubiquitous connectivity and run powerful `Apps' on today's Smart phones requires a front-end radio able to handle tremendous data rates; and that, requires access to the full bandwidth owned by service providers. Once, the front-end radio consisted of a single power amplifier (PA), filter/duplexer, a switch and a low noise amplifier (LNA). Early on, a cell phone might be able to access 2 or 3 frequency bands. Today, the iPhone 7 accesses 23 to 24 GSM, CDMA and LTE frequency bands, while the Galaxy flag ship phones from Samsung have 16 bands (not counting the GPS, Wi-Fi, Bluetooth and NFC radios). Power amplifier, Low noise amplifier and switch functions can be combined-important for cost and size - but, proliferation of usable bands has driven up filter count. New bands are being created (opening up more frequency spectrum) and more challenging; existing bands are now being combined in what is called Carrier Aggregation. This requires better performance from the filter and also drives filters to become smaller as handset manufacturers struggle to add more filters into a limited space. This has created (in just a few years) a whole new billion dollar industry focused on building high quality ultra-miniature filters; An industry where better quality filters enable better wireless communication, which-in turn-drives the technology to build better filters.

Using first principles and the constitutive equations for a piezoelectric, we solve the 2-D acoustic wave inside a single, infinite, piezoelectric membrane to study the dispersion of thin film bulk acoustic resonator (FBAR) lateral modes, with and without infinitely thin electrodes. The acoustic eigenfunction is a dual wave, composed of longitudinal and shear components, able to satisfy the 2-D acoustic boundary conditions at the vacuum interfaces. For the single piezoelectric slab, we obtain analytical expressions of the dispersion for frequencies near the longitudinal resonant frequency (Fs) of the resonator. These expressions are more useful for the understanding of dispersion in FBARs and more elegant than numerical methods like finite-element modeling and various matrix methods. We additionally find that the interaction between the resonator's electrodes and the acoustic wave modifies the lateral-mode dispersion when compared to the case with no electrodes. When correctly accounting for these interactions, the dispersion zero is placed clearly at Fs, unlike what is calculated from a 2-D model without electrodes where the dispersion zero is placed at Fp. This is important since all experimental evidence of measures FBAR resonators shows that the dispersion zero is at Fs. Furthermore, we introduce an electrical current-flow model for the propagating acoustic wave inside the electroded piezoelectric, and based on this model, we can discuss an electrode-loss mechanism for FBAR lateral modes which depends on dispersion. From our model, it results that lateral modes with real k(x) have higher electrode dissipation if they are closer to the resonant frequency. This is consistent with the typical behavior of measured FBAR filters where the maximum lateral mode damage on the insertion loss takes place for frequencies immediately below Fs.

The past decades' phenomenal and rapid growth in cell phone use and, more recently, in smartphone adoption is apparent to everyone. What has not be so clearly articulated is that underlying this growth is a larger growth in the demand for smartphone filters and duplexers. As a result of fourth-generation longterm evolution wireless technology (4G)-and in light of coming fifth-generation (5G) requirements-the number of filters needed in smartphones has exploded.

We present a robust, chip-scale packaged FBAR oscillator that is compatible with high volume manufacturing. The oscillator's extremely small size (area <; 1 mm2, thickness = 0.23 mm) combined with an SMT-compatible pad design enables integration of the timing function in-package with a companion ASIC. We have measured tens of thousands of oscillators operating at a native frequency of 2.6 GHz and observe mean jitter less than 10 fsec (12 kHz to 20 MHz offset), with many devices better than 8 fsec. The mean phase noise is -158 dBc/Hz at 800 kHz offset and -118 dBc/Hz at 10 kHz offset. The device draws 18 mA at 3.3V, and the phase noise at all frequency offsets remains within 1 dB over the temperature range from -40 to 125°C. Far from carrier noise is set by the power delivered to the resonator. Due to the ability of the resonator to remain linear at high power, far-from-carrier phase noise is as low as -165 dBc/Hz. The sensitivity to acceleration of these oscillators is better than 0.1 ppb/g. Hermeticity tests carried out on the chip-scale package indicate that the oscillators behave with the same level of integrity as our standard FBAR filters. Preliminary studies on aging have determined an upper bound on frequency drift. Including contributions from supply and load sensitivity, temperature, and aging, total frequency drift is less than +/-200 ppm.

We present a FBAR oscillator that operates at 628MHz, achieves low jitter <;50fs and good frequency stability all while fitting in a small package of 1.1 × 0.9 × 0.25 mm3. The chip-scale oscillator employs a feedback circuitry in the encapsulating lid of a FBAR resonator and makes use of a differential Colpitts oscillator design fabricated in 0.6μm CMOS technology. To achieve the frequency precision required for a reference oscillator, we demonstrate the ability to tune the oscillator over 700ppm using a switched capacitor scheme to compensate for manufacturing tolerances. For achieving frequency stability over temperature and packaging stress, the FBAR resonators used in these oscillators employ silicon dioxide layer temperature compensation and a stress relieved structure respectively. The measured integrated jitter (12kHz to 20MHz) for the oscillators with a supply voltage of 3.3V across a wafer is 33fs with a far from carrier phase noise of -170dBc/Hz .The median current draw from the supply is 16.5mA and the output power measured at a 50ohm load using a balun is 0dBm.These oscillators are suitable for co-integration as reference clocks in high speed communication ICs where size and performance are paramount.

We present a fourth-design generation Free Running Oscillator and Voltage Controlled Oscillator using integrated bipolar circuitry in the lid wafer with a temperature-compensated FBAR resonator in the base wafer. The goal is to produce a high frequency, low-noise oscillator. Because there are ~15,000 oscillators per wafer, we can develop very sensitive testing procedures to study the oscillator behavior. For example, we have determined our frequency measurement accuracy and precision to be ~ 0.2 parts-per-million (1 σ), and our phase sensitivity floor to be less than -180 dBc/Hz. Measurements on package hermeticity, suggest that the oscillators behave with the same level of integrity as our standard FBAR filters.

We describe a Band 13 FBAR duplexer that uses a temperature compensated Tx die to allow for `co-existence' between the transmit function of the hand set and the public safety band (PSB) used by first responders.

One of the issues facing many types of oscillators is the transference of stress from the external world through the die to the resonator. Typically, resonators are clamped at more than one location. Integrated FBAR oscillators (referred to as FMOS1,2), uses a resonator that is clamped on all sides and integrated into an all-silicon, chip-scale package with integrated circuits. For filter applications, this is quite reasonable, but, for oscillators this may not be acceptable. Mounting FBAR oscillators (epoxy die attach, over-molding and soldering) onto a customer board exposes the FBAR oscillator to stresses that occur during the assembly, plus additional stresses that occur during the wear and tear (as well as temperature induced stresses) that the customer board experiences. Although intuitively, applied stress will change frequency of the resonator, this is hard to quantify. This paper does a first cut model of the stresses and then matches that to the changes in the measured frequency. Next, we discuss several designs that help mitigate the effect of external stresses on the resonator.

This paper focuses on the technical differentiation of film bulk acoustic resonator (FBAR) technology from other mechanical resonator technologies for timing applications. The paper will touch on a recent modification of FBARs, the zero-drift resonator (ZDR), that is temperature compensated. One technology differentiator is the size of the chip-scale packaged resonator. Another is that the silicon lid is perfectly suitable for placement of integrated circuits and this is currently being done. Many factors (wide tuning range, high Q, high frequency, small size, integrated circuitry) are being used to differentiate potential products for the time and frequency markets.

July 31st, 2001, Avago (then Agilent) shipped its first 25,000 FBAR duplexers (in tape & reel) for nCDMA mobile phones. The value proposition was size (relative to the ceramic duplexers used at that time). At the time, it was supposed that FBAR technology using AlN as the active piezo material would not last beyond a few years. SAW technology, already entrenched in the lower frequencies and with better economies of scale and lower technology barrier to commercialization should have quickly made FBAR a `short-lived' technology. Although still a possibility, FBAR has persevered for over 10 years due to several reasons; high Q, small size, ability to form an all-silicon package (utilizing silicon-fab technology) and reliability. However, the next 10 years pose a challenge to FBAR and serious innovation is necessary so that a similar talk about the success of FBAR covering 20 years can be given. Innovation must cover the ability to go differential, temperature compensation, continued Q enhancement, and chip-scale packages to spread the cost of manufacturing and research. This talk will touch on each of these subjects as well as giving an overview of the unique set of circumstances that made FBAR as successful as it is.

Recent advances in temperature-compensation for FBAR (Film Bulk Acoustic Resonators) have brought this technology forward as a serious contender in the oscillator marketplace. As with any mechanical resonator oscillator, a cost-effective hermetic package combined with circuit technology are critical for commercial application. Billions of FBAR duplexers have been fabricated using Avago Technologies' wafer-scale packaging process, whereby a silicon lid wafer is Au-diffusion-bonded to a base FBAR wafer to make a robust, hermetic package. This paper presents a method for integrating circuitry into the lid wafer to form a sub-0.1 mm(3), sub mW, 1.5 GHz temperature-compensated chip-scale oscillator. Circuit integration, testing and performance will be discussed.

Most ASIC (Application Specific Integrated Circuits) chips have a common need for clocking. The clock is usually supplied by the end-user of the ASIC chip and consists of a quartz crystal resonator, two precision capacitors, and an on-chip inverter driver. An ASIC supplier that can integrate the clock inside their package will have a product differentiator relative to their competitors. We demonstrate a zero drift FBAR Resonator (ZDR) with a native Q of 3000 and a temperature stability of ±50 ppm integrated with a CMOS oscillator core, all bias circuitry, oscillator buffer, dividers, and output buffer. The 0.6μm node CMOS circuitry is integrated in the silicon lid of the microcapped device. Since many thousands of packaged die are created on each wafer, one can take a significant amount of statistics on the effect of frequency shift due to environmental stress (HAST, Autoclave, thermal shock). This allows us to accurately quantify aging effects as well as the most likely forms of device failures in the field.

Recently, a new standard has been proposed to augment the performance of future Global Positioning System (GPS) receivers, and is generally referred to as the Global Navigation Satellite System (GNSS) band. By also requiring differential signals from the output of the filter to the cell phone receiver, further performance improvements can be obtained. To accommodate the new GNSS specifications and to provide single-ended to differential (SE-DE) mode conversion, new filter designs are required. In this work, we describe a two-stage, SE-DE filter design for GNSS that is based on coupled resonator filter (CRF) technology. The design provides insertion loss better than -2.5 dB over a frequency range greater than 56 MHz. Out-of-band rejection is greater than 40 dB from DC to 6 GHz, and better than 60 dB below 2 GHz. As a stand-alone filter, excellent phase and amplitude balance are achieved without the need for external inductors. In a frontend module consisting of the filter and an Avago LNA, we have measured >;13 dB gain over the GNSS band. The module also shows excellent rejection and true differential output equivalent to surface acoustic wave filter solutions.

First results on a novel voltage controlled oscillator (VCO) in the lower gigahertz range, featuring excellent phase noise and high power efficiency are presented. The heart of the VCO is a recently reported novel miniature two-pole decoupled stacked bulk acoustic resonator (DSBAR) filter. With its single 180° phase transition over the 1 dB bandwidth, linear phase, and maximum 1 dB insertion loss, it provides stable single-mode operation over 45 MHz (≈3%) of tuning bandwidth and has negligible heat dissipation when operated at incident power levels of 100 mW or greater. The 1.55-GHz laboratory VCO prototypes operate at 5 V supply voltage, 50 mA supply current, 15 dBm of output power, and >13% efficiency, demonstrating -84 and < -180 dBc/Hz phase noise suppression at 1 kHz carrier offset and in the thermal noise region, respectively. VCOs with cascaded DSBAR filters for further phase noise reduction are also demonstrated.

This paper presents a wide-tuning digitally controlled FBAR-based oscillator in a 0.18μm CMOS process. The oscillator is tuned with a digitally-switched capacitor array to achieve a tuning range of >7000ppm, an over eight-fold improvement over previously published low power FBAR-based VCOs. The high Q FBAR allows frequency tuning to be implemented with a switched-capacitor array with relatively large unit capacitors to achieve a sufficiently fine resolution for frequency synthesis. Our oscillator achieves a measured phase noise of -99dBc/Hz and -142dBc/Hz at 10kHz and 1MHz offsets respectively at a carrier frequency of 1.50GHz while consuming less than 4mW.

Coupled resonator filters designed using a single-layer coupler require coupling materials with an acoustic impedance less than 5.0 MRayl. Carbon-doped oxide, with an acoustic impedance of 4.8 MRayl and an acoustic attenuation of 200 to 600 dB/cm at 1 GHz, can be used as a single-layer coupler to produce a competitive 2-stage coupled resonator filter for cellular handset applications in the gigahertz frequency range. The electrical response of our filter is superior to that of coupled resonator filters using a traditional acoustic mirror as the coupling element. We present an ultra-miniature 0.58 mm x 0.38 mm coupled resonator filter operating at a frequency of 2.15 GHz.

When comparing different resonator technologies, it is essential that fundamental properties such as the unloaded Q be accurately portrayed. Important Figure-of-Merit (FOM) numbers for resonators include operating frequency, coupling coefficient (kt2), Q, and the products - kt2*Q and f*Q. Three of the five Figure's of Merit depend on an accurate evaluation of unloaded Q. Using a new equation for Q (derived from first principles), we can measure both Q and the coupling coefficient for a variety of resonator technologies and compare the relative performance metrics of each technology.

This letter reports a passively temperature-compensated CMOS oscillator utilizing a film bulk acoustic resonator. The resonator exhibiting an f ldr Q product of 2-4 X 10 12 s -1 is composed of molybdenum, aluminum nitride, and a compensation material that has a positive temperature coefficient of Young's modulus. The 604-MHz oscillator consumes 5.3 mW from a 3.3-V supply and achieves excellent phase noise performances of -102, -130, and -149 dBc/Hz at 1, 10, and 100 kHz carrier offsets, respectively. The oscillator's temperature-dependent frequency drift is less than 80 ppm over a temperature range of -35degC to +85degC.