We review some emerging trends in transduction, connectivity and data analytics for Point-of-Care Testing (POCT) of infectious and non-communicable diseases. The patient need for POCT is described along with developments in portable diagnostics, specifically in respect of Lab-on-chip and microfluidic systems. We describe some novel electrochemical and photonic systems and the use of mobile phones in terms of hardware components and device connectivity for POCT. Developments in data analytics that are applicable for POCT are described with an overview of data structures and recent AI/Machine learning trends. The most important methodologies of machine learning, including deep learning methods, are summarised. The potential value of trends within POCT systems for clinical diagnostics within Lower Middle Income Countries (LMICs) and the Least Developed Countries (LDCs) are highlighted.

Lamb wave delay lines with acoustoelectri-cally-induced non-reciprocity are demonstrated in suspended lithium niobate-on-silicon waveguides for the first time. An electric current is fed through the silicon layer in the same axis as the piezoelectrically-transduced acoustic waves which are attenuated or amplified depending on the direction of the energy exchange with drifting electrons (i.e. acoustoelectric (AE) effect). Therefore, the insertion loss (IL) and non-reciprocity of the delay line is adjustable by controlling the current bias which varies the electron drift velocity and the subsequent momentum transfer. Proof-of-concept delay lines in the range of 600 MHz to 700 MHz are demonstrated with a fractional bandwidth as high as 2.8% and AE gain as high as 5.6 dB resulting in ~20 dB of non-reciprocity. These non-reciprocal components could offer a monolithic and dynamically-tunable solution to the numerous issues that arise from the increasing congestion and interferences in the telecommunication spectrum and suggests the possibility of developing fully-switchable low-IL delay lines through design/fabrication optimizations.

In this paper, Thickness-Lamé (TL) mode piezoelectrically-transduced silicon resonators are studied and demonstrated. It will be shown that unlike Planar-Lamé resonance modes, Thickness-Lamé modes could be efficiently excited using sputtered polycrystalline piezoelectric films such as Scandium Aluminum Nitride (ScAlN) due to the constructive contribution of both d₃₁ and d₃₃ piezoelectric coefficients in the coupling coefficient. Moreover, it is shown through finite element analysis and experimental results that the coupling coefficient improves with the order of the TL harmonic mode excited in a silicon slab. It is also confirmed that the quality-factor of TL resonators substantially enhances through utilization of properly-designed acoustic reflectors (i.e. acoustic isolation frames) around the tethered resonator block. The temperature coefficient of frequency is also modeled using finite-element eigen-frequency analysis. It is shown that the turnover temperature of TL resonators aligned to the [100] plane of a degenerately-doped n-type silicon substrate varies considerably as the mode shape transitions from a Thickness-Lamé to a Lateral-Extensional mode with the gradual increase of wavelength to thickness ratio. A record Q of 23.2k is measured for a ~185MHz fundamental TL resonator in vacuum (fxQ=4.3x 10¹²) while quality factors of 12.6k (fxQ=4.6x 10¹²) and 6k are also measured in vacuum for second- and third-harmonic TL resonators at 326 MHz and 555 MHz respectively. The combination of high turnover temperatures (>80 °C), high quality factor, and low motional resistance, promises the suitability of such resonators for extremely-stable oven-controlled oscillator applications. [2019-0263]

This work explores micromachined heterostructured waveguides that leverage strong interactions between acoustic phonons and electrons to enable radio frequency (RF) signal amplification or attenuation. A thin-film piezoelectric-on-semiconductor stack is tailored to generate high electromechanical coupling Lamb waves that are impacted by high mobility electrons within a microacoustic waveguide. Lamb waves are generated by RF signal via interdigital electrodes on the piezoelectric layer; by applying a voltage to the semiconductor layer so that the electrons lead mechanical waves, the RF signal is amplified through the acoustoelectric (AE) effect. Conversely, the signals propagating faster or in the opposite direction of the electron flow undergo attenuation, rendering the waveguide nonreciprocal. Research on the AE effect dates to the mid-20th century and until now has been mostly focused on surface acoustic waves (SAWs). In this work, enabled by high-quality bonded thin films of lithium niobate (LN) and silicon (Si), it is shown that fundamental symmetric ( $S$ 0) Lamb mode waveguides at 100 s of MHz can achieve more than 40 dB of AE gain and strong nonreciprocal transmission with less than 10 mW of bias power consumption. This could enable implementation of switches, delay lines, isolators, and circulators, which are critical for interference cancellation and full-duplex radio. The AE effect is observed to be stronger in some higher $S$ 0 harmonics, allowing for scaling to higher frequencies with optimized electrodes that have more relaxed critical dimensions. In addition, up to 5.5-dB sustained terminal gain measured in this work implies the potential for transistor-less amplifiers that could be implemented in concert with more traditional acoustic devices in a single-chip manner.

In this work we demonstrate that it is possible to push the most dominant sources of extrinsic loss (i.e. anchor and air loss) in high-frequency thin-film piezoelectric-on-substrate (TPoS) MEMS resonator to levels that they no longer limit the overall Q. This is achieved through altering the substrate regions around the resonators, etching notch and reflector structures, so that the resulted acoustic cavity is virtually not leaking acoustic energy once the resonator is operated in vacuum. We experimentally prove our technique by presenting an 1100% improvement in Q for a TPoS resonator operating at ~82 MHz and achieving an f×Q of 2.6×10 ¹² .

In this article, the microfluidic channels that deliver liquid to a microscale thin-film piezoelectric-on-silicon (TPoS) gravimetric resonant sensor are incorporated into the backside of the silicon-on-insulator (SOI) wafer on which the resonator is fabricated. Specifically, a microwell is embedded at the bottom of the disk -shaped TPoS resonator, while a very thin layer of parylene covering the backside of the resonator and the microwell forms an isolation layer between the liquid and the top device-layer features. In this way, the liquid is in contact with the backside of the resonator, while the device-defining trenches and the electrical connections to the resonator stay clear, thus mitigating the acoustic energy loss and undesirable feedthroughs. The impact of the parylene layer thickness on a few symmetric ( ${S}$ ) and antisymmetric ( ${A}$ ) Lamb wave modes of the resonator is experimentally studied, and the performance of such modes in the liquid is characterized by filling the microwells through a PDMS-based microfluidic channel. The parylene layer, while marginally affecting the resonator in the air, is found to substantially enhance its performance in the liquid media. Strong resonance peaks with high quality factors ( ${Q}$ ) are observed for the ${S}$ modes, among which ${Q}$ values above 400 are recorded for a specific mode named ${S}$ ( 4 , 2 ) (among the highest ever reported). This article can potentially facilitate the realization of highly stable and sensitive resonant mass sensors (i.e., microbalance) for real-time applications. Additionally, the effect of the acoustic energy radiation in the form of evanescent shear and longitudinal waves in liquid on the ${Q}$ and resonance frequency of the disk resonators is experimentally validated.