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... which each period of the transducer is modelled as a sectional equivalent circuit. Acoustic transmission line elements are introduced to model the wave propagation, while ideal transformers are included to account for the piezoelectric transduction. The model was modified as in [10] to include the aforementioned discontinuity in phase velocity. Fig. 5 shows the equivalent circuit used to represent each period of the transducer, with denoting the acoustic impedance of the free LiNbO3 film and denoting the acoustic impedance of the metallized LiNbO3 film. and are related ...
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In this paper, we propose an electrically tunable coupling filter that utilizes orthogonal gratings together with graphene. The position of the transmission valley can be altered by varying the gate voltage's strength, and the electrotunable properties of lithium niobate are described. Under resonance conditions, monolayer graphene is comparable to...
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... Acoustic waves in contrast, travel roughly five orders of magnitude more slowly than EM waves, thus enabling lithographic definition of wavelength-scale features and significant time delays at RF frequencies of interest. As a result, acoustic waves in piezoelectric solids have been widely utilized in the implementation of delay lines [5,6], transversal filters [7,8], correlators [9][10][11], convolvers [12], and other analog signal processing devices [13]. While acoustic propagation losses are typically lower than in EM counterparts, devices requiring large time-bandwidth products (TBP) can still undergo signal degradation due to significant time delays. ...
Signal processing with the use of acoustic waves is an important technology for various functions in RF systems, including matched filtering in congested parts of the frequency spectrum. In order to generate long time delays on chip required for these applications, the acoustoelectric effect offers the ability to counter acoustic propagation losses while also generating inherent non-reciprocity. In this work, we demonstrate an approach to directly bond thin film silicon from 200-mm commercial SOI wafers on X-cut lithium niobate substrates with the use of plasma surface activation. The resulting delay line devices at 410 MHz demonstrate amplification of Rayleigh waves, with a peak non-reciprocal contrast between forward and reverse traveling waves of over 25 dB/mm under continuous DC bias conditions. The demonstrated process can extend the functionality of traditionally passive piezoelectric RF microsystems.
... For the latter approach, acoustic delay lines are well suited for generating significant delays in a small form factor on chip, thanks to the significantly lower velocity at which acoustic waves travel compared to RF electromagnetic waves. Acoustic delay lines also demonstrate high RF power handling, which has enabled demonstrations of matched filtering implemented by correlators [7], [8]. This can complement a circulator in the RF front end in generating transmitter suppression for IBFD systems. ...
... Among various types of acoustic devices, acoustic delay lines (ADLs) have been demonstrated with diverse applications ranging from transversal filters [18], [19] and correlators [20]- [22] to oscillators [23], sensors [24], [25], and amplifiers [26]- [28], alongside the recent prototypes of time-domain equalizers [29] and time-varying non-reciprocal systems [30]. Conventionally, ADLs are built upon surface acoustic wave (SAW) platforms [31]- [33]. ...
We present the first group of acoustic delay lines (ADLs) at 5 GHz using the first-order antisymmetric (A1) mode in Z-cut lithium niobate thin films. The demonstrated ADLs significantly surpass the operation frequencies of the prior art with similar feature sizes because of their simultaneously fast phase velocity, large coupling coefficient, and low loss. In this article, the propagation characteristics of the A1 mode in lithium niobate are analytically modeled and validated with finite element analysis. The design space of A1 ADLs is then investigated, including both the fundamental design parameters and those introduced from the practical implementation. The implemented ADLs at 5 GHz show a minimum insertion loss of 7.9 dB, an average insertion loss (IL) of 9.1 dB, and a fractional bandwidth around 4%, with group delays ranging between 15 and 109 ns and the center frequencies between 4.5 and 5.25 GHz. The propagation characteristics of A1 mode acoustic waves have also been extracted for the first time. The A1 ADL platform can potentially enable wideband high-frequency passive signal processing functions for future 5G applications in the sub-6-GHz spectrum bands.
... Third, the recent development of high electromechanical coupling (k 2 ) piezoelectric platforms [7]- [13] has demonstrated record-low loss over a wide bandwidth (BW), thus overcoming the high insertion loss (IL) and narrow bandwidth bottleneck that has been precluding acoustic signal processing from eMBB applications. Among different acoustic devices at RF, acoustic delay lines (ADL) have been demonstrated for a wide range of applications, including transversal filters [14], [15], correlators [16], timedomain equalizers [17], oscillators [18], sensors [19], amplifiers [20], [21], and time-varying non-reciprocal systems [22]. These diverse signal processing functions can all be implemented by tailoring the transducers [23] and waveguides [24]. ...
We present the first group of GHz broadband SH0 mode acoustic delay lines. The implemented acoustic delay lines adopt unidirectional transducer designs in a suspended X-cut lithium niobate thin film. The design space of the SH0 mode acoustic delay lines at GHz is first theoretically investigated, showing that the large coupling and sufficient spectral clearance to adjacent modes collectively enable the broadband performance of SH0 delay lines. The fabricated devices show 3-dB fractional bandwidth ranging from 4% to 34.3%, insertion loss between 3.4 dB and 11.3 dB. Multiple delay lines have been demonstrated with center frequencies from 0.7 GHz to 1.2 GHz, showing great frequency scalability. The propagation characteristics of SH0 in lithium niobate thin film are experimentally extracted. The demonstrated acoustic delay lines can potentially facilitate broadband signal processing applications.
... Among various types of acoustic devices, acoustic delay lines (ADL) have been demonstrated with diverse applications ranging from transversal filters [16], [17] and correlators [18]- [20] to oscillators [21], sensors [22], [23], and amplifiers [24]- [26], alongside the recent prototypes of time domain equalizers [27] and time-varying non-reciprocal systems [28]. Conventionally, ADLs are built upon surface acoustic wave (SAW) platforms [29]- [31]. ...
We present the first group of acoustic delay lines (ADLs) at 5 GHz, using the first-order antisymmetric (A1) mode in Z-cut lithium niobate thin films. The demonstrated ADLs significantly surpass the operation frequency of the previous works with similar feature sizes, because of its simultaneously fast phase velocity, large coupling coefficient, and low-loss. In this work, the propagation characteristics of the A1 mode in lithium niobate is analytically modeled and validated with finite element analysis. The design space of A1 ADLs is then investigated, including both the fundamental design parameters and those introduced from the practical implementation. The implemented ADLs at 5 GHz show a minimum insertion loss of 7.94 dB and a fractional bandwidth of 6%, with delays ranging between 15 ns to 109 ns and the center frequencies between 4.5 GHz and 5.25 GHz. The propagation characteristics of A1 mode acoustic waves have also been extracted for the first time. The A1 ADL platform can potentially enable wide-band high-frequency passive signal processing functions for future 5G applications in the sub-6 GHz spectrum bands.
... Recently, nonreciprocal [5], [6] and switchable acoustic delay lines have generated great interest in the research community for application in full duplex radio networks [7], [8]. Improvements in materials processing have also enabled demonstrations of acoustic wave devices with very high electromechanical coupling [9], [10] that may be implemented in correlators [11], [12] or delay lines for the RF front end. Hence, a robust fabrication process for generating integrated AE amplifiers to compensate acoustic propagation losses in such devices remains of great interest. ...
... An ADL is then used to impose delays to the incoming signal as a function of its frequency to perform matched filtering for demodulation of the signal. Naturally, such a function of ADLs can be also dual-purposed as a modulator on the transmitter side [7]- [9]. ...
... The overall mechanic reflection coefficient of an electrode can be found by summing the multiple reflections produced by the step-up and step-down discontinuities. Referencing the reflections to the center of the electrode, we attain the expression Γ = Γ e jα (1 − e −j2α ∑(Γ e −jα ) 2 ∞ =0 ) (9) where α is the phase retardation for traversing half the width of a reflector. α is 3 /4 for DART and /2 for EWC reflectors. ...
... Introducing to (9) and simplifying the geometric series, we obtain ...
This paper demonstrates low-loss acoustic delay lines (ADLs) based on shear-horizontal waves in thin-film LiNbO
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for the first time. Due to its high electromechanical coupling, the shear-horizontal mode is suited for producing devices with large bandwidths. Here, we show that shear-horizontal waves in LiNbO
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thin films are also excellent for implementing low-loss ADLs based on unidirectional transducers. The high acoustic reflections and large transducer unidirectionality induced by the mechanical loading of the electrodes on a LiNbO
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thin film provide a great tradeoff between delay line insertion loss and bandwidth. The directionality for two different types of unidirectional transducers has been characterized. Delay lines with variations in the key design parameters have been designed, fabricated, and measured. One of our fabricated devices has shown a group delay of 75 ns with an IL below 2 dB over a 3-dB bandwidth of 16 MHz centered at 160 MHz (fractional bandwidth = 10%). The measured insertion loss for other devices with longer delays and different numbers of transducer cells are analyzed, and the loss contributing factors and their possible mitigation are discussed.
... The designed ADLs were fabricated with the process described in [16]. magnitudes of the ripples) in group delay are lessened for an ADL with a larger transducer gap because it is compositionally more of an un-metalized LiNbO3 thin film waveguide with smaller overall dispersion. ...
... These devices have very high electromechanical coupling and have been extended to enable resonant devices and circuits that include high figure of merit resonators [22]- [26], low loss wide-band filters [27]- [29], wide-range tunable oscillators [30], and high gain voltage transformers [31], [32]. Non-resonant devices such as wideband low loss dispersive delay lines for chirp compression [33]- [35], and frequency correlators for orthogonal frequency coding [36] have also been demonstrated for exploiting the signal processing capabilities of LiNbO3. However, PnCs have not been explored so far for LiNbO3 lateral modes. ...
... An equivalent circuit model shown in Fig. 7 has been constructed to model input and output transducers. The model is based on the Mason's model, of which more details can be found in [36], [55]. In this model, a sectional equivalent circuit [ Fig. 7(b)] represents a pair of half electrodes and the LiNbO3 thin film in-between and underneath [ Fig. 7(a)]. ...
... Instead of embedding scatter matrices, a 60-μm-long acoustic transmission line is inserted between the input and output to represent the short section of LiNbO3 thin film. Distributed attenuators [omitted in Fig. 7(c)] are also included in the model to emulate the propagation loss in the fabricated devices [36]. Additional loss of acoustic energy also occurs after the acoustic waves traverse the transducers and are subsequently scattered or absorbed by the substrate. ...
This paper reports the first demonstration of phononic crystals (PnCs) in suspended lithium niobate thin films, which exhibit band gaps for tailoring the performance of laterally vibrating devices. Transmission and reflection properties of lithium niobate phononic crystals for both shear-horizontal (SH0) and lengthextensional (S0) modes have been investigated and subsequently explored in two applications. In the first case, PnC-embedded delay lines were designed for filtering with stopbands, while in the second case, PnC-bounded resonators were implemented for spurious mode suppression. Equivalent circuit models incorporating acoustic scattering parameters of the designed PnCs and the Mason’s model of the transducers have been built for each application. Benchmarked to reference devices without PnCs, the measured PnCs embedded in delay lines show 20 dB attenuation in the stop-bands and less than 2 dB loss in the pass-bands for the SH0 mode, and 30 dB attenuation in the stop-bands and less than 10 dB loss in the pass-bands for the S0 mode. The fabricated piezoelectric PnC-bounded resonator has shown a quality factor of 434 at 142.7 MHz with undesired spurious modes significantly suppressed. These demonstrations show that lithium niobate PnCs for laterally vibrating devices can potentially lead to wide-band and low-loss acoustic functions for radio frequency signal processing.
... Use of SAWs in piezoelectric substrates is beneficial due to the inherently short wavelengths of acoustic waves at radio frequencies (RF), in addition to supporting the power levels and dynamic range required for signal processing. In the intervening years, improvements in fabrication and material quality have enabled operation of acoustic wave devices for correlation with low insertion losses and the ability to work directly with high frequency RF signals [5], [6]. ...
This paper describes the use of Lithium Niobate and GaN on sapphire substrates to define SAW correlators for direct sequence spread spectrum modulation. Passive correlators with maximal length sequence periods of 7 and 15 are fabricated and tested on 128° Y-cut bulk Lithium Niobate. The input transducer is modulated at carrier frequencies of 470-930 MHz with a chip duration of 100 ns. At the output, a maximum peak-to-sidelobe ratio of 15 dB is measured. The same design is then fabricated in GaN on sapphire in order to incorporate acoustoelectric gain sections using an AlGaN barrier engineered to ensure low sheet density. We consider a basic cell consisting of a tap followed by a gain section to support long correlator structures. This represents a first step towards mitigating acoustic propagation losses in monolithic GaN SAW correlators.
