Rich Ruby

A Temperature-Stable Film Bulk Acoustic Wave Oscillator

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 1012 s-1 is composed of molybdenum, aluminum nitride, and a compensation material that has a positive temperature coefficient of Youngs 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 oscillators temperature-dependent frequency drift is less than 80 ppm over a temperature range of -35degC to +85degC.

Method of Extracting Unloaded Q Applied Across Different Resonator Technologies

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 Figures 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.

Coupled resonator filter with single-layer acoustic coupler

We discuss the operation of novel coupled-resonator filters with single-layer acoustic couplers. Our analysis employs the physical Mason model for acoustic resonators. Their simpler fabrication process is counterbalanced by the high acoustic attenuation of suitable coupler materials. At high levels of attenuation, both the phase and the acoustic impedance must be treated as complex quantities to accurately predict the filter insertion loss. We demonstrate that the typically poor near-band rejection of coupled resonator filters can be improved at the die level by connecting a small capacitance between the input and output of the filter to produce a pair of tunable transmission minima. We make use of these theoretical findings to fabricate coupled resonators filters operating at 2.45 GHz.

Ultra-miniature coupled resonator filter with single-layer acoustic coupler

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 times 0.38 mm coupled resonator filter operating at a frequency of 2.15 GHz.

A decade of FBAR success and what is needed for another successful decade

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.

A wide-tuning digitally controlled FBAR-based oscillator for frequency synthesis

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.

11E-3 A Thermally Stable CMOS Oscillator Using Temperature Compensated FBAR

This paper presents a passively temperature compensated CMOS oscillator utilizing Film Bulk Acoustic Resonator (FBAR). The resonator exhibiting f-Q product of 2~3times1012 sec-1 is comprised of molybdenum (Mo), aluminum nitride (AlN), and a compensation material that has positive temperature coefficient of Youngs modulus. The 600 MHz oscillator consumes 6.6 mW from a 3.3 V supply and achieves an excellent phase noise performance of -102 dBc/Hz, -132 dBc/Hz, and -151 dBc/Hz at 1 kHz, 10 kHz, and 100 kHz carrier offset, respectively. The oscillators temperature-dependent frequency drift is less than 80 parts per million (ppm) over a temperature range of -35 to +85degC.

Method of fitting Q-circles of measured mechanical resonators

When calculating and publishing Q values of mechanical resonators, there is a certain amount of uncertainty that exists as to the validity of the Q value claim. When different resonator technologies are compared, one concern is the method of Q extraction and the impact of local calibration. Recently, as Avago continues to make improvements in Q, the values for Rp (now closing in on 10,000Ω) becomes more questionable and a method must be put in place that gives one the best accuracy. In this work, it is assumed that any fundamental resonance can be modeled using the modified Butterworth Van Dyke (mBVD) type circuit [1]. A ‘best practices’ will be proposed.

Low jitter FBAR based chip scale precision oscillator

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.

FBAR resonator figure of merit improvements

Free-standing Bulk Acoustic Resonator (FBAR), as one type of bulk acoustic wave (BAW) devices, has extremely high Q to enable excellent filter performance, and has been successfully applied to the wireless communication market. The Bode equation to calculate the unloaded Q is used to map the Avago FBAR product line resonator Rp values. The manufacturing Rp values from old and new generations of FBAR products are collected and compared to demonstrate the importance of the figure of merit (FOM) improvements.