With the increased performance requirements for film bulk acoustic resonator (FBAR) devices, accurate test of FBAR device parameters has become critical. The key of the FBAR on-board test is its test fixture structure and de-embedding methods. In this paper, the research status of FBAR board testing technology is reviewed. The parasitic effects, impedance matching and clamping design of the test fixture structure design process are discussed. The principle and error model of de-embedding and the advantages/disadvantages of each calibration method are analyzed. The accuracy of FBAR on-board test can be improved by reducing parasitic effects, optimizing impedance matching, improving calibration methods, and optimizing error model.
Defects in efficiency or usability have come into being when using the maximum stress on FBAR structure as the reference stress or using the so called “Calculus-like analysis method” to calculate the sensitivity of FBAR transducer. The former does not consider the influence of the strain in the thickness direction, which overestimates the sensitivity. The latter learns from FEM, but it is too complicate and heavy-workload. In order to eliminate these deficiencies, the improved sensitivity prediction method for FBAR transducer is put forward. The whole calculation process is completed with COMSOL FEM software to avoid the complex data processing. The energy weighted average method is used to calculate the average strain of every single layer in FBAR and the average internal pressure of piezoelectric layer. The average strain is used to modify the thickness of FBAR, and the internal pressure is used to modify the elastic constant of piezoelectric material. Then the eigenfrequency solving method is carried out to solve the eigenfrequency of FBAR. The former improves the speed of solving, and the latter enhance the accuracy of the calculation results. The sensitivity of both circular membrane type FBAR transducer and FBAR micro-accelerometer can be calculated through the improved method. The expected sensitivity of the membrane type FBAR transducer is 46.5 MHz/N, which is close to the experimental result, 50 MHz/N. However, due to unawareness of the actual structure parameters, the expected sensitivity of the micro-accelerometer is 27 kHz/g, which is different from the experimental result, 100 kHz/g. The two calculation cases indicate that the improved sensitivity prediction method for FBAR transducer is both effective and available.
In order to determine the order of BAW ladder filter, the relationship among out-of-band rejection, area ratio of parallel and series FBAR, and the filter order N are studied by simulating. Based on FBAR Mason model, firstly, one-order to six-order BAW ladder filters are constructed; next, the area ratio of parallel and series FBAR (Cps) is set from 1 to 6, and the six BAW ladder filters are simulated in ADS; finally, the left out-of-band rejections are extracted from the simulation result, and plotted as a graph. In addition, as the filter orders can be set to a half order, the filters with order N (N=1.5… 5.5) are simulated in the same way. Simulation results show that the out-of-band rejection has an equal increase with the filter order in number when Cps remains constant, and that the out-of-band rejection increases as Cps increases when filter order keeps constant. When optimizing the design, the area ratio of parallel and series FBAR (Cps) is usually set from1 to 4, within which the out-of-band rejection will increase by about 10 dB when the filter increases by one order. And when the filter increases half order, the out-of-band rejection will increase by 5 dB, which is about half of the value by increasing an integer order. In addition, the structure of ladder filter is discussed, and the influence of the filter order and capacitance ratio on the passband performance is studied.
Microstrip interdigital filter requires use of grounding via-holes, but the grounding via-holes will influence performance of interdigital filter. The traditional design method does not consider grounding via-holes effect in the initial design process, which will lead to some uncertainties of the grounding via-holes, such as the number, the size and the position. This will make the subsequent optimization face multi-factor and multi-level problems. In addition, when the substrate thickness and the center frequency increase to a certain extent, the external quality factor obtained by using the traditional 50 Ω tapped-line cannot reach the theoretical value. Therefore, the traditional design method is modified, and the grounding via-holes effect is considered in the initial design process by using 3D electromagnetic field simulation software. When the traditional 50 Ω tapped-line do not meet the design requirements, it is improved to a gradual tappedline with the combination of a 50 Ω microstrip line and a narrower microstrip line. Taking a Ka-band filter as an example, 100 μm and 300 μm thick high resistance silicon are used as substrate respectively. The simulation results indicate that the initial design for filter with the modified method is closer to the specifications, which can reduce subsequent iterations. Besides, the insertion loss of filter with gradual tapped-line is 1.91 dB, and return loss is 18.06 dB. What’s more, the stop rejection at 27.00 GHz and 33.40 GHz are 46.91 dB and 59.58 dB, respectively.
In order to predict the thermal behavior of bulk acoustic wave resonator (BAWR) and evaluate the power handling capacity, a BAWR thermal behavior simulation method is proposed. The conductor surface loss in the BAWR electromagnetic model is extracted and used as the heat source for thermal simulation to obtain the temperature distribution of the resonator. Then the signal feeding edge, active area shape and power handling capacity are researched. The simulation results show that in order to moderate the self-heating effect of BAWR, the signal feeding should follow the principle of “feeding in from long edge, feeding out from long edge”; active area shape has little to do with selfheating effect; the power handling capacity of the designed BAWR can reach to 3 W.
The resonant sensors based on aluminum nitride double-ended tuning fork (AlN DETF) have the characteristics of small size, good stability and reliability, fast response. In order to improve the sensitivity and resolution, it is necessary to analyze the influence of the structure parameters of vibrating beam on the sensitivity and signal power of AlN resonator. The multi-physics model of AlN DETF resonator was established to verify effect of single parameter on the sensitivity by pre-stressed eigenfrequency analysis. The relationships between signal power and length, width of vibrating beam were obtained by post-processing data of simulation results when the thickness remained constant. The results show that relative sensitivity and signal power are growing with opposite direction with the width or the length of the beam. Therefore, there is a design tradeoff between signal power and relative sensitivity of AlN resonator according to the process and structure strength. The optimized AlN DETF resonator was simulated, its sensitivity, signal power and Q are 56 Hz/μN, 6.8e-4 nW and 958, respectively.
An S band narrowband bandpass filter BAW with center frequency 2.460 GHz, bandwidth 41MHz, band insertion loss - 1.154 dB, the passband ripple 0.9 dB, the out of band rejection about -42.5dB@2.385 GHz; -45.5dB@2.506 GHz was designed for potential UAV measurement and control applications. According to the design specifications, the design is as follows: each FBAR’s stack was designed in BAW filter by using Mason model. Each FBAR’s shape was designed with the method of apodization electrode. The layout of BAW filter was designed. The acoustic-electromagnetic cosimulation model was built to validate the performance of the designed BAW filter. The presented design procedure is a common one, and there are two characteristics: 1) an A and EM co-simulation method is used for the final BAW filter performance validation in the design stage, thus ensures over-optimistic designs by the bare 1D Mason model are found and rejected in time; 2) An in-house developed auto-layout method is used to get compact BAW filter layout, which simplifies iterative error-and-try work here and output necessary in-plane geometry information to the A and EM cosimulation model.
A high-performance aluminum nitride (AlN) differential resonant accelerometer is proposed. The inertia force of the proof mass is amplified to improve the sensitivity by two-stage microlever; the cross sensitivity is reduced by I-shape supporting beam; and the differential frequency detection scheme is used to decrease the effect of temperature common mode error. The accelerometer is mainly composed of proof mass, supporting beam, two-stage microlever and resonator, and its structural parameters are optimized by theoretical analysis and finite element simulation. The modal analysis shows that the fundamental frequencies of the two resonators are approximately 373.3 kHz, and the frequency differences from the interferential modes are about 9.4 kHz, which effectively achieves mode isolation. According to the simulation results of sensitivity, the sensitivity, linearity and cross sensitivity of AlN differential resonator accelerometer are 64.6 Hz/g, 0.787% and 0.0033 Hz/g, respectively. The simulation results of thermal stress show that the temperature sensitivity of a single resonator is about 490 Hz/°C, and the temperature sensitivity of output differential frequency is - 0.83 Hz/°C, which demonstrate that the differential frequency detection scheme can reduce the influence of temperature common mode error. All the above simulation results prove that this structural design of the accelerometer is feasible.
In order to ensure the normal operation of mobile devices in the Wi-Fi band without interference from adjacent frequency bands, a BAW filter for the Wi-Fi 802.11b band (2402-2482 MHz) is designed. An initial structure ladder filter based on a one-dimensional Mason equivalent circuit model of thin-film bulk acoustic resonator (FBAR) is designed. The resonance area value of series FBARs and the ratio of resonance area value of parallel FBARs to series FBARs are made into two types of optimization parameters reasonably. According to the required insertion loss and out of band rejection of filter as the optimization objective, the optimized values are obtained by the algorithm based on gradient and genetic in ADS software. In order to make the simulation results more accurate, the combined acoustic-electromagnetic method is used to simulate and compare with the simulation results of the Mason equivalent circuit model in the filter design process. The results show that the performance of the filter is decreased, insertion loss increased 1.6 dB, ripple increased 1.1 dB, out of band rejection is basically the same. The design of Wi-Fi band BAW filter has low insertion loss (less than 3 dB) and high out of band rejection (more than 40 dB) performance.
Experiment shows that thin film bulk acoustic resonator (FBAR) is feasible to detect gamma irradiation, but the sensing mechanism is not studied deeply. For this problem, different sensing mechanisms are proposed to explain the resonance frequency shift after gamma irradiation according to two different FBAR structures. One FBAR structure is four - layers stacked (metal layer - piezoelectric layer - oxide layer - metal layer). After gamma irradiation, a voltage will be formed in the radiation sensitive layer (oxide layer), which is equivalent to impose a DC voltage to the piezoelectric layer that makes resonant frequency shift. There is a semiconductor layer between oxide layer and piezoelectric layer in the other FBAR structure, which is the difference between the two structures. A voltage formed in the oxide layer after irradiation will change the surface potential of the semiconductor and then change the space charge layer capacitor in semiconductor that makes the resonant frequency shift. The results of two mechanisms are obtained by simulation and compared with those in related literature, it is found that the trends and magnitudes of frequency shift are the same, so the two mechanisms are feasible.
In order to reduce the volume of the filter and increase the number of chips on the wafer, while ensure the filter performance, a design method of the bulk acoustic wave (BAW) ladder filter is proposed. This layout design method consists of 11 design criteria and a 6-step flow. The 11 design criteria limit the shape and position of the BAW resonators (BAWRs), the distance between the BAWRs, the distance between the BAWRs and the pads and the interconnecting wire. The layout design flow has 6 steps. 1) Preset the shape of each BAWR (square/pentagon) according to its active area values. 2) Add an auxiliary circumcircle for each BAWR, tightly align all the series resonator circumcircles along a central line in order, and mate the corresponding electronically neighboring parallel resonator circumcircles one by one at a position above/below the center line. This makes an initial 3-row and <i>n</i>-column 2D arrangement, and the column number N is determined by the filter order. 3) Fix the very first series resonator circumcircle position and incrementally “compress” the initially self-assembled 3-row structure along the row width direction until the row height for row width bargain is no more cost effective. 4) Apodize the square series resonators and fine-tune each resonator’s shape and rotation according to above-mentioned related design criteria. 5) Wiring BAWRs and pads together. 6) A combined acoustic-electromagnetic BAW filter simulation method is used to validate the layout result. In a 5-order BAW ladder filter layout demo case, a layout fill ratio over 44% is obtained. An auto-layout program “BAW-filter Auto-layout Tool (BAT<sup>®</sup>)” based on the presented method is also presented.
Bulk Acoustic Wave Resonators (BAWRs) have been well developed both as filters and as high sensitivity sensors in recent years. In contrast to traditional megahertz quartz resonators, BAWRs offer significant increases in resonant frequency, typically operating in gigahertz regimes. This translates into a potential sensitivity increase of more than three orders of magnitude over traditional QCM (Quartz Crystal Microbalance) devices. Given the micrometer-scale size of BAW sensor-head, read-out circuitry can monolithic integrated with this GHz transducer is urgently needed to produce small, robust, and inexpensive sensor systems. A BAW sensor read-out circuit prototype based on Pierce oscillator architecture is fulfilled in this paper. Based on the differential measurement scheme, two uniform BAWRs are used to constitute two BAW oscillators as a reference and a measurement branch respectively. The resonant frequency shift caused by the measurand is obtained by mixing and filtering the two oscillator signals. Then, the intermediate signal is amplified, shaped and converted to a digital one. And a FPGA is used for frequency detection. Taking 2 GHz BAW mass sensor as a case study, deign procedure are given in details. Simulation and experimental results reveal a 0-99 MHz frequency shift measurement range. Main factors affecting phase noise of the BAW oscillator (i.e. mainly frequency stability of the BAW sensor readout circuit) are also discussed for further optimizations.
In order to obtain the high-fidelity model of latching failure threshold power of the capacitive RF MEMS switch, it is necessary to find out the rough dielectric layer effect on its down-state capacitance degradation. The comparative modeling method between the 3-D electromagnetic simulation and the equivalent circuit simulation is proposed. First, the simulation curve of the switch isolation (S<sub>21</sub>) is attained at different roughness levels with the HFSS 3-D electromagnetic model. And then the simulation curve of the S<sub>21</sub> of the ADS equivalent circuit model is consistent with the simulation result of the 3-D electromagnetic as far as possible by tuning the down-state capacitance in the equivalent circuit. Hence, the relationship between the dielectric layer roughness and the down-state capacitance is identified. By changing the roughness level of dielectric layer and repeating the above steps, the relationship between the dielectric layer roughness and the down-state capacitance degradation is identified. Rationality and feasibility of the method is verified by comparing the calculated values of the down-state capacitance with the measured values in a relevant literature. And analytical equation of the latching failure threshold power of the capacitive RF MEMS switch with perfect smooth dielectric layer is modified, according to the relationship between the dielectric layer roughness and the down-state capacitance degradation, which is also suitable for predicting the power handling capacity of the switch with rough dielectric layer.
This paper presents a new linear inertial acceleration switch which senses inertial
acceleration and gives a signal of switchpoint. It is an entire mechanical device has two particular
characters: a simple structure and an environmental interference-free capability. The structure and
work principle of the switch is introduced, then the design process to the spring is analyzed and
simulated, and finally the rationality of this acceleration switch's design is given according to the
sample's testing data.
In this acceleration switch, the elastic component is a leaf spring, and the mass component
is a standard steel ball. The spring and the ball are separated instead of rigidly connected, which
make the whole structure is simple. When the switch is on the work direction the ball and the
spring are interact, and the spring is on work; when the switch isn't on the work direction, the ball
and the spring are separated; environmental external force is on the mass instead of on the spring.
The spring is insusceptible on this condition. This particularity determines that the switch is highly
environmental interference-free, and doesn't easily affected by environmental influence.
Some parameters of the inertial switch are given as followings: (1) Overall dimension of the
inertial switch is about 28mm×12mm×12mm; (2) systemic precision of the inertial switch is 1.5%;
(3) the inertial switch can endure 0.2g<sup>2</sup>/Hz stochastic vibration. It is suggested that this inertial
switch can be applied in high consequence system.
The optical fiber delivery laser power technology in laser flexible manufacturing system is introduced.
The characteristics of optical fiber delivery Nd:YAG pulsed laser power through multimode silica fiber
are experimentally researched, which include beam spatial characteristics of fiber exit beam and the
capacity of optical fiber delivery high power laser. The effects of laser injection condition and optical
fiber bending radius on optical fiber delivery laser beam system are analyzed. The morphology
characterization of laser induced damage to optical fiber end-faces were measured and investigated.
The model of laser induced damage to fiber end faces is presented.
A novel coupling method for injecting a high peak power laser into a multimode optical fiber through cone-channel condenser is introduced. The novel coupler is investigated by experiments and theories. The design minimizes the irradiance on the fiber input face and reduces its dependence on the system alignment. A simple lens and a special designed cone-channel condenser operate together to transform a laser beam with 5 mm diameter into a smaller one that fits on the 400 μm or 600 μm diameter fiber face. The method resolves the problem that laser induce damage to fiber input end faces. The design principle and method of cone-channel condenser are described by the light transmission theory. The prototype was fabricated without anti-reflection coatings on the end faces. The experimental results show that the transmission efficiency of cone-channel condenser is up to 90%. Though there was 1 mm gap between the cone-channel condenser and a fiber, the coupling efficiency of cone-channel condenser to fiber reach 73%. The maximum transmitted energy before front-face of cone-channel condenser breakdown is 84.5mJ. The transmission capacity of fiber increases by 2-3 times comparing with the traditional method. The interest in this new coupling method is related to the development of transmitting high peak powers through multimode fibers applied to laser-based firing systems for initiating explosives and driving flyer, et al.
For laser detonator application, high-peak power pulsed Nd:YAG laser is transmitted through all-silica optical fiber. The
transmission properties of step-index fibers are investigated, using a high-peak power pulsed Nd: YAG rod laser with
beyond 1MW power and Q-switch mode. The fibers are step-index multimode fibers with 400 or 600 μm core diameters,
440 or 660 μm cladding diameters. The power delivery characteristics were studied by theory and experiments. The
results show that the fiber core diameter, NA, length and so on affect the transmission efficiency for high power laser.
When the laser power is beyond a certain threshold, the SRS and SBS will be serious; the quantity of fiber end-face
limits to the raising of laser power passing through fibers; the zero-probability damage threshold is calculated according
to ISO/DIS standard 11254-1.2, which is 58.6J/cm<sup>2</sup>. Energy distribution of output beam from fibers will be uniform.
Even the fiber end-face was partly damaged, laser power is still deliverable, and the transmission efficiency is related to
the fiber damage grade.
With the development of DWDM, optical analysers which are portable and can be applied to DWDM project site, are in
great demand. This paper describes a novel method for wavelength fine-selection. This new method employs a refractive
optical lever system, the structure of which is simple. It also has low cost and enough feasibility. This is a significant
improvement not only on the wavelength discrimination capability of optical spectrum analysers for demanding DWDM
test applications, but also on technology of frequency stabilization of lasers. We firstly demonstrate the refractive optical
lever principle of a wedge prisms and the amplification factors for wedge prisms with different wedge angles. Secondly,
the feasible experiment is done, the aim of which is improving the wavelength selecting accuracy of the optical spectrum