J. F. Ribeiro

Thermoelectric generator and solid-state battery for stand-alone microsystems

This paper presents a thermoelectric (TE) generator and a solid-state battery for powering microsystems. Prototypes of TE generators were fabricatedand characterized. The TE generator is a planar microstructure based on thinfilms of n-type bismuth telluride (Bi 2Te 3) and p-type antimony telluride (Sb 2Te 3), which were deposited using co-evaporation. The measurements on selected samples of Bi 2Te 3and Sb 2Te 3thinfilms indicated a Seebeck coefficient in the range of 90–250 ¹ V K −1 and an in-plane electrical resistivity in the range of 7–17 ¹A m. The measurements also showed TEfigures-of-merit, ZT, at room temperatures (T =300 K) of 0.97 and 0.56, for thinfilms of Bi 2Te 3and Sb 2Te 3, respectively (equivalent to a power factor, PF, of 4.87 mW K −2 m −1 and 2.81 mW K −2 m −1 ). The solid-state battery is based on thinfilms of: an anode of tin dioxide (SnO 2), an electrolyte of lithium phosphorus oxynitride (Li xPO yNz, known as LiPON) and a cathode of lithium cobaltate (LiCoO 2, known as LiCO), which were deposited using the reactive RF (radio-frequency) sputtering. The deposition and characterization results of these thin-films layers are also reported in this paper. (Somefigures in this article are in colour only in the electronic version)

Design and manufacturing challenges of optogenetic neural interfaces: a review

Optogenetics is a relatively new technology to achieve cell-type specific neuromodulation with millisecond-scale temporal precision. Optogenetic tools are being developed to address neuroscience challenges, and to improve the knowledge about brain networks, with the ultimate aim of catalyzing new treatments for brain disorders and diseases. To reach this ambitious goal the implementation of mature and reliable engineered tools is required. The success of optogenetics relies on optical tools that can deliver light into the neural tissue. Objective/Approach: Here, the design and manufacturing approaches available to the scientific community are reviewed, and current challenges to accomplish appropriate scalable, multimodal and wireless optical devices are discussed. SIGNIFICANCE Overall, this review aims at presenting a helpful guidance to the engineering and design of optical microsystems for optogenetic applications.

A flexible Li-ion battery with design towards electrodes electrical insulation

The application of micro electromechanical systems (MEMS) technology in several consumer electronics leads to the development of micro/nano power sources with high power and MEMS integration possibility. This work presents the fabrication of a flexible solid-state Li-ion battery (LIB) (~2.1 μm thick) with a design towards electrodes electrical insulation, using conventional, low cost and compatible MEMS fabrication processes. Kapton® substrate provides flexibility to the battery. E-beam deposited 300 nm thick Ge anode was coupled with LiCoO2/LiPON (cathode/solid-state electrolyte) in a battery system. LiCoO2 and LiPON films were deposited by RF-sputtering with a power source of 120 W and 100 W, respectively. LiCoO2 film was annealed at 400 °C after deposition. The new design includes Si3N4 and LiPO thin-films, providing electrode electrical insulation and a battery chemical stability safeguard, respectively. Microstructure and battery performance were investigated by scanning electron microscopy, electric resistivity and electrochemical measurements (open circuit potential, charge/discharge cycles and electrochemical impedance spectroscopy). A rechargeable thin-film and lightweight flexible LIB using MEMS processing compatible materials and techniques is reported.

A chemically stable PVD multilayer encapsulation for lithium microbatteries

This work was financially supported by FEDER/COMPETE and FCT funds with the projects PTDC/EEA-ELC/114713/2009, PEST-C/QUI/UI0686/2013 and UID/EEA/04436/2013, first author scholarship SFRH/BD/78217/2011, fourth author scholarship SFRH/BPD/95905/2013, and CRUP AI TC-09_14.

Electrical insulation properties of RF-sputtered LiPON layers towards electrochemical stability of lithium batteries

Electrochemical stability, moderate ionic conductivity and low electronic conductivity make the lithium phosphorous oxynitride (LiPON) electrolyte suitable for micro and nanoscale lithium batteries. The electrical and electrochemical properties of thin-film electrolytes can seriously compromise full battery performance. Here, radio-frequency (RF)-sputtered LiPON thin films were fabricated in nitrogen plasma under different working pressure conditions. With a slight decrease in the deposition pressure from 6 to 1 × 10−3 mbar, the 600 nm thick LiPON film reveals an electric resistivity increase from 108 to 1010 Ω cm, respectively. UV– micro-Raman spectroscopy confirms the nitrogen incorporation on the Li3PO4 material, while scanning electron microscopy, Rutherford backscattering spectrometry and nuclear reaction analysis show a well-defined compact structure with a composition of Li2.2PO2.2N0.6 for the higher electrical-resistivity film. An ionic conductivity close to 3 × 10−7 S cm−1 at room temperature (22 °C) was measured by AC impedance spectroscopy. Thermal properties were investigated through the differential scanning calorimetry technique. LiPON films reveal high optical transmission (>75%) in the UV–vis range, which could be interesting for transparent electronic devices.

Thin Films for Thermoelectric Applications

The introduction of nanotechnology opened new horizons previously unattainable by thermoelectric devices. The nano-scale phenomena began to be exploited through techniques of thin-film depositions to increase the efficiency of thermoelectric films. This chapter reviews the fundamentals of the phenomenon of thermoelectricity and its evolution since it was discovered in 1822. This chapter also reviews the thermoelectric devices, the macro to nano devices, describing the most used techniques of physical vapor depositions to deposit thermoelectric thin-films. A custom made deposition chamber for depositing thermoelectric thin films by the thermal co-evaporation technique, where construction issues and specifications are discussed, is then presented. All the steps for obtaining a thermoelectric generator in flexible substrate with the custom deposition chamber (to incorporate in thermoelectric microsystems) are described. The aim of thermoelectric microsystem relays is to introduce an energy harvesting application to power wireless sensor networks (WSN) or biomedical devices. The scanning probe measuring system for characterization of the thermoelectric thin films are also described in this chapter. Finally, a few of the prototypes of thermoelectric thin films (made of bismuth and antimony tellurides, \({\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}\), and \({\mathrm{Sb}}_{2}{\mathrm{Te}}_{3}\), respectively) obtained by co-evaporation (using the custom made deposition chamber) and characterized for quality assessment are dealt with. All the issues involved in the co-evaporation and characterization are objects of analysis in this chapter.

High aspect-ratio neural probes using conventional blade dicing

Exploring deep neural circuits has triggered the development of long penetrating neural probes. Moreover, driven by brain displacement, the long neural probes require also a high aspect-ratio shafts design. In this paper, a simple and reproducible method of manufacturing long-shafts neural probes using blade dicing technology is presented. Results shows shafts up to 8 mm long and 200 µm wide, features competitive to the current state-of-art, being its outline simply accomplished by a single blade dicing program. Therefore, conventional blade dicing presents itself as a viable option to manufacture long neural probes.

All-solid-state batteries: An overview for bio applications

Batteries are crucial for most of bio applications. Batteries based on a liquid or polymer electrolyte needs a weight protective packaging which decreases their energy density and increases their size. This paper aims to identify, on the one hand, the efforts performed in thin-film batteries until now, and on the other hand, to provide an overview about the future perspectives in integration of batteries with flexible electronic circuits and energy harvesting systems. The overview highlights the need for an on-going investigation that aims to replace metallic lithium anode of batteries through different approaches. Other materials, namely silicon or germanium, seem promising when combined with nanostructures. Three dimensional and integrated batteries will increase its volumetric capacity.

Stereoscopic image sensor with low-cost RGB filters tunned for the visible range

This paper presents a low-cost technology for fabricating optical filters arrays tuned for the primary colors. The fabrication process presented in this paper is intended for directly printing the optical filters into a transparent flexible substrate (acetate). The target application of these optical filters is for enabling the acquisition of multicolor stereoscopic images with a sensor made in CMOS technology.

A new implantable wireless microsystem to induce mictrition in spinal injury patients

This paper presents a new wireless microsystem for for use in urology. This microsystem is composed by two parts: the electrostimulation and the radio-frequency (RF) subsystems. The electrostimulation part is a silicon box with groves to pass the nerves to be stimulated. Above the stimulation box is putted a cover containing electrodes to do the electrical contacts with the nerves. Using wafer-level packaging (WLP) techniques the RF and the electrostimulation parts are joined together. This implantable microsystem allows the reception of RF signals with user commands to activate the micturition function and the penian erection (on males) patients. The microsystem has an expected area of 5×5 mm2.