Martha Small

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.

High coupling coefficient Temperature compensated FBAR resonator for oscillator application with wide pulling range

This paper demonstrates two variations of Temperature compensated (TempCo) FBAR resonators with high Kt². One 1.5 GHz non-symmetric stack design TempCo FBAR resonator has a Kt² of 4.28% and linear TCF of 0 ppm/°C. A second, quasi-symmetric stack design 1.5GHz TempCo FBAR resonator has Kt² as high as 5.6% and linear TCF of −6 ppm/°C. Significant Kt² improvement comes from optimal design of stack film, interposer electrode effect and novel process development of a sealant for the oxide to protect it from HF etching. This paper also discusses the trade-off between two parameters (linear TCF vs. Kt²). High Kt² TempCo FBAR resonator is ideal for FBAR oscillator application with wide frequency pulling range.

An ultra-miniature, low cost single ended to differential filter for ISM band applications

We present a filter for the 2.4 GHz ISM band that has both filtering and balun functionality to deliver a single ended to differential (SE2DE) filter response and 4:1 impedance transformation. We integrate the balun and filter response into a single chip using two FBAR resonators stacked one on top of the other and separated by a thin, low acoustic impedance material. True SE2DE behavior is achieved by dividing the bottom FBAR into two 100 Ohm resonators and hooking them in parallel to present a 50 Ohm impedance to the endpoint. The two 100 Ohm resonators forming the top of the stack are connected in series to present a differential output impedance of 200 Ohms. Since the entire device is not much larger than a single 50 Ohm resonator, the total die size is extremely small (much smaller than a typical FBAR half ladder filter utilizing 4 to 8 resonators).

7E-2 A De-Coupled Stacked Bulk Acoustic Resonator (DSBAR) Filter With 2 dB Bandwidth > 4%

Coupled resonator filters extend the use of classical FBAR/BAW filters by enabling them to convert single-ended signals into differential signals while using a much smaller wafer real estate. In lieu of the traditional multi-layer de-coupling structure we introduce a novel technique in which only a single thin polymer layer with appropriate acoustic impedance is used. In the de-coupled stacked bulk acoustic resonator design (DSBAR) we demonstrate a 0.4 x 0.5 mm single-ended filter operating at 2.45 GHz with a bandwidth at the 2 dB points of greater than 4%, in-band return loss of less than -10 dB and excellent out-of-band rejection. Cross-wafer variation and the temperature response of these filters are shown.

A fully integrated wafer-scale sub-mm 3 FBAR-based wireless mass sensor

A wireless sub-mm3 FBAR-based mass sensor fully integrated in a hermetic package is demonstrated. We propose a wafer-scale commercially viable manufacturing process for the integration of the sensor and the interface circuitry. The drift in frequency of the FBAR sensor due to temperature, aging and stress is reduced by a factor of 10 through an integrated differential measurement. The sensor achieves a sensitivity of 0.45kHz.cm2/ng and consumes 14.7mW including the wireless link. The operation of the sensor has been demonstrated in thin film deposition and wireless humidity sensing experiments.

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.

Manufacturing and reliability of chip-scale packaged FBAR oscillators

We present a robust, chip-scale packaged FBAR oscillator that is compatible with high volume manufacturing. The oscillators 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.

Sub-10 fs jitter S-band oscillators and VCOs in a 1×1×0.23 mm3 chip scale package

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.

A 48 MHz, hermetic, 0.48 mm 2 chip-scale packaged USB3.0 oscillator integrating an FBAR resonator with CMOS circuitry

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.