Frank Bi

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.

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.

Thickness control by ion beam milling in acoustic resonator devices

In this paper, practical aspects of production worthy methods for film uniformity adjustment (trimming) used in manufacturing of Film Bulk Acoustic Resonator (FBAR) filters [1], [2] have been presented. Two-step trimming in conjunction with thickness “smoothing” technique control total thickness range to within less than 8A on product wafers with variable surface film etch rates even with difficult to measure film thickness. Trimming processes were used to allow using one wafer from a batch to provide compensation feedback in the FBAR devices. Combining ion mill with deposition in the same tool produces <0.1% uniformity in the deposited films.

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 2.6 GHz, 25 fs jitter, differential chip scale oscillator that is 2 in area and 0.25mm tall

We demonstrate a 2.6 GHz chip-scale oscillator that measured phase noise better than -150 dBc/Hz at 1 MHz offset and integrated jitter of just 25 fs. The part was designed with differential out and drives a 100 Ohm differential load with a mean voltage swing of 100 to 200 mV. The phase noise at 10 kHz offset is -110 dBc/Hz. The device runs at 3.3V and Idd is just over 9mA (including buffer). Another variant is designed to have an on-chip varactor allowing tuning of 615 ppm/V over the targeted 0.5 to 1.8 V tuning range. Here, the integrated jitter degrades by 2X at 0 V Vtune and we measured 85 fs jitter at 1.5 V Vtune. Still, the integrated jitter was well below 100 fs. The all-silicon packaged part is designed to directly solder down onto a PCB. There are no bond wires used in the assembly of this device. The height of the soldered part is under 0.25 mm, and the area of the die is less than 1 mm2. The oscillator uses a Zero Drift Resonator (ZDR) FBAR and we see about +/- 100 ppm temperature drift from -40C to +110°C. The design uses a cross-coupled architecture with the ZDR and is ac-coupled to a buffer amplifier.

Effects of FBAR resonator dissipated power on discrete oscillator phase noise

We present single-ended and balanced configurations of modified Colpitts voltage controlled oscillators utilizing zero drift FBARs that are compatible with high volume manufacturing. These oscillators have been built with resonators spanning frequencies between 384 MHz and 3900 MHz, demonstrating that temperature compensated FBAR is useful over a decade frequency range for oscillator applications. Over the 1 GHz to 2.5 GHz range, we have observed mean jitter less than 10 fsec (integrated over a 12 kHz to 20 MHz offset), with the best devices demonstrating performance of 5.5 fs. The resonator is 27,000 square microns in a .43 × .35 × .23 mm package. The oscillators are designed to support a temperature range from -40 to 85°C. Due to the ability of the resonator to remain linear at dissipated power values up to 25 mW, far-from-carrier phase noise as low as -185 dBc/Hz @ 10 MHz has been achieved.

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.