Development of Capacitive-Type Sensors by Electrochemical Anodization: Humidity and Touch Sensing Applications

This work describes the development of a capacitive-type sensor created from nanoporous anodic aluminium oxide (NP-AAO) prepared by the one-step anodization method conducted in potentiostatic mode and performed in a low-cost homemade system. A series of samples were prepared via an anodization campaign carried out on different acid electrolytes, in which the anodization parameters were adjusted to investigate the effect of pore size and porosity on the capacitive sensing performance. Two sensor test cases are investigated. The first case explores the use of highly uniform NP-AAO structures for humidity sensing applications while the second analyses the use of NP-AAO as a capacitive touch sensor for biological applications, namely, to detect the presence of small “objects” such as bacterial colonies of Escherichia Coli. A mathematical model based on equivalent electrical circuits was developed to evaluate the effect of humidity condensation (inside the pores) on the sensor capacitance and also to estimate the capacitance change of the sensor due to pore blocking by the presence of a certain number of bacterial microorganisms. Regarding the humidity sensing test cases, it was found that the sensitivity of the sensor fabricated in a phosphoric acid solution reaches up to 39 (pF/RH%), which is almost three times higher than the sensor fabricated in oxalic acid and about eight times higher than the sensor fabricated in sulfuric acid. Its improved sensitivity is explained in terms of the pore size effect on the mean free path and the loss of Brownian energy of the water vapour molecules. Concerning the touch sensing test case, it is demonstrated that the NP-AAO structures can be used as capacitive touch sensors because the magnitude of the capacitance change directly depends on the number of bacteria that cover the nanopores; the fraction of the electrode area activated by bacterial pore blocking is about 4.4% and 30.2% for B1 (E. Coli OD600nm = 0.1) and B2 (E. Coli OD600nm = 1) sensors, respectively.

A MEMS Ultra-Wideband (UWB) Power Sensor with a Fe-Co-B Core Planar Inductor and a Vibrating Diaphragm Capacitor

The design of a microelectromechanical systems (MEMS) ultra-wideband (UWB) RMS power sensor is presented. The sensor incorporates a microfabricated Fe-Co-B core planar inductor and a microfabricated vibrating diaphragm variable capacitor on adhesively bonded glass wafers in a footprint area of 970 × 970 µm2 to operate in the 3.1–10.6 GHz UWB frequency range. When exposed to a far-field UWB electromagnetic radiation, the planar inductor acts as a loop antenna to generate a frequency-independent voltage across the MEMS capacitor. The voltage generates a coulombic attraction force between the diaphragm and backplate that deforms the diaphragm to change the capacitance. The frequency-independent capacitance change is sensed using a transimpedance amplifier to generate an output voltage. The sensor exhibits a linear capacitance change induced voltage relation and a calculated sensitivity of 4.5 aF/0.8 µA/m. The sensor can be used as a standalone UWB power sensor or as a 2D array for microwave-based biomedical diagnostic imaging applications or for non-contact material characterization. The device can easily be tailored for power sensing in other application areas such as, 5G, WiFi, and Internet-of-Things (IoT). The foreseen fabrication technique can rely on standard readily available microfabrication techniques.

Parametric oscillation and amplification with gate controlled capacitor-within-capacitor

Parametric oscillators and parametric amplifiers are known for their ‘quiet’ operation and find new applications in quantum circuitry. A Capacitor-within-Capacitor (CWC) is a nested electronic element that has two components: the cell (e.g., the outer capacitor) and the gate (e.g., the inner capacitor). Here we provide analysis and experiments on diode-interfaced, CWC that exhibit parametric oscillations and parametric amplifications. By replacing the diode with a doped nano-graphene junction, we demonstrated a new structure whose doping may be electronically and chemically controlled. Advantages of these elements are in their simplicity, large relative capacitance change (of the order of 50%), separation of pump and signal channels and possibility for large integration.

Design and electromechanical properties of three-layer fabric-based pressure sensor

In this study, we developed a three-layer fabric-based pressure sensor and analyzed the structural factors and design parameters that affect its electromechanical properties. The sensor has a three-layer fabric and angle interlocking structure, which enhance its structural stability, sensing capability, and durability. Based on the factors that affect the sensing properties of the fabric sensor, 12 fabric sensors were designed. The electromechanical properties of these sensors were analyzed by adjusting the warp density and material of the three-layer fabric structure, as well as the weft yarn type of the dielectric layer. The curve showing the efficiency of the fabric sensor was divided into three zones, namely, elastic, yield, and crush, to investigate the frequency-response properties, linear variation range, sensitivity, and stability of the fabric sensor. The results indicated that the warp density and warp and weft yarn types of the dielectric layer of the sensor affected the capacitance change rate and sensitivity. The effects of the weft yarn type of the dielectric layer on the electromechanical properties of the fabric sensor were complex. Additionally, the woven and angle interlocking structures of the three-layer fabric sensor contributed to the electrical stability and durability of the sensor. In the design of a multilayer flexible fabric sensor, the appropriate warp density, as well as the warp and weft materials, should be considered to ensure its linearity, sensitivity, and repeatability.

Ceramics, materials, microelectronics and graph theory new frontiers

This research is focused on further developing of application and use of graph theory in order to describe relations between grains and to establish control over layers. We used functionalized BaTiO3 nanoparticles coated with Yttrium-based salt. The capacitance change results on super-microstructure levels are the part of the measured values on the bulk samples. The new idea is graph theory application for determination of electronic parameters distribution at the grain boundary and to compare them with the bulk measured values. We present them with vertices in graph, corresponding with grains, connected with edges. Capacitance change with applied voltage was measured on samples sintered in air and nitrogen, up to 100 V. Using graph theory, it has been shown that capacitance change can be successfully calculated on the layers between grains. Within the idea how to get parameters values at microlevel between the grains and pores, mathematical tool can be developed. Besides previously described 1D case, some original calculations for 2D cases were performed in this study, proving successful graph theory use for the calculation of values at nanolevel, leading to a further minituarization in micropackaging.

Failure Mechanism of Multilayer Ceramic Capacitors under Transient High Impact

In recent years, penetrating weapons have been used more and more to attack increasingly hard targets; therefore, the impact of such a penetrating process has increased to an extremely high level. As an important component of a fuze, the reliability of the ceramic capacitor in high-impact environments is key for the normal working of the fuze. In this paper, we found that a high-impact causes parameter drift of the multilayer ceramic capacitor (MLCC), which further causes the fuze to misfire. This paper mainly studies the internal mechanism of the MLCC’s parameter drift during high impact. Firstly, transient physical phenomena, such as capacitance fluctuation and the leakage current increase of the ceramic capacitor under a high acceleration impact, were studied experimentally by a Machete hammer, revealing the relationship between the capacitance change, leakage current change, and acceleration under different working conditions. Secondly, a mechanical model of the ceramic capacitor is established to simulate the change in capacitance value, which shows that the main factor of the capacitance change is the deformation-derived change in the facing area between the electrodes. Lastly, an equivalent circuit model is established to simulate the change in the leakage current, which shows that the main factor of the leakage current change is the piezoelectric resistance of the ceramic dielectric.

AC and DC Differential Bridge Structure Suitable for Electrochemical Interfacial Capacitance Biosensing Applications

This paper presents a capacitive differential bridge structure with both AC and DC excitation and balancing capability for low cost electrode-solution interfacial capacitance biosensing applications. The proposed series RC balancing structure offers higher sensitivity, lower susceptibility to common-mode interferences, and drift control. To evaluate the bridge performance in practice, possible effects of initial bridge imbalance due to component mismatches are investigated considering the required resolution of the balancing networks, sensitivity, and linearity. This evaluation is also a guideline to designing the balancing networks, balancing algorithm and the proceeding readout interface circuitry. The proposed series RC bridge structure is implemented along with a custom single frequency real-time amplification/filtering readout board with real-time data acquisition and sine fitting. The main specifications for the implemented structure are 8-bit detection resolution if the total expected fractional capacitance change at the interface is roughly 1%. The characterization and measurement results show the effectiveness of the proposed structure in achieving the design target. The implemented structure successfully achieves distinct detection levels for tiny total capacitance change at the electrode-solution interface, utilizing Microcystin-(Leucine-Arginine) toxin dilutions as a proof of concept.

Plasmon-Coupled Photocapacitor Neuromodulators

Efficient transduction of optical energy to bioelectrical stimuli is an important goal for effective communication with biological systems. For that plasmonics has significant potential via boosting the light-matter interactions. However, plasmonics has been primarily used for heat-induced cell stimulation due to membrane capacitance change (i.e., optocapacitance). Instead, here we demonstrate that plasmonic coupling to photocapacitor biointerfaces improves safe and efficacious neuromodulating displacement charges for an average of 185% in the entire visible spectrum while maintaining the Faradaic currents below 1%. Hot-electron injection dominantly leads the enhancement of displacement current at blue spectral window, and nanoantenna effect is mainly responsible for the improvement at red-spectral region. The plasmonic photocapacitor facilitates wireless modulation of single cells at 3-orders of magnitude below the maximum retinal intensity levels corresponding to one of the most sensitive optoelectronic neural interfaces. This study introduces a new way of using plasmonics for safe and effective photostimulation of neurons and paves the way toward ultra-sensitive plasmon-assisted neurostimulation devices.