All-printed low-power metal oxide gas sensors on polymeric substrates

This paper presents a novel approach for the fabrication of miniaturized and fully printed metal-oxide (MOX) gas sensors on a polyimide (PI) substrate by using digital manufacturing of the functional layers, namely aerosol jet and inkjet printing technologies. We are reporting a stacking approach for all-printed MOX sensors for the first time. High resolution (similar to 20 mu m) printing of metallic patterns is enabled by aerosol jet of gold nanoparticles in solution, which leads to printed resistive thermal transducers with a reduced size of 500 x 500 mu m(2). The wide area printing feature of the aerosol jet is also applied for printing a thin (similar to 2 mu m) inter-dielectric PI layer in between the heater and gold electrodes. The gas sensing layer, i.e. Pd-doped tin oxide (SnO2) nanoparticles, is deposited through drop on demand inkjet printing. Proper operation of the printed sensors is evaluated in both dry and humid conditions under reducing and oxidizing gases i.e. CO and NO2, respectively. All the tests are performed at 250 degrees C, produced by the integrated micro-hotplate at a low power consumption of similar to 78 mW. The chemo-resistive responses of the sensors towards both the gases are found to be in the acceptable range as compared to conventional metal-oxide gas sensor responses. These results are very promising for future integration of MOX gas sensors notably in smart printed electronics, disposable systems and wearables.

Remote Powering and Wireless Communication of a Smart Knee Prosthesis

Oguz Atasoy

With the advance in microelectronics and microsystems, better instruments in every domain are designed and built. For many years, scientists have tried to understand nature, and engineers to mimic the perfect design. One example of this is the human knee, which is usually a very long-lasting joint. Due to accidents, infection and misuse, some patients need to have total knee replacement surgery. Therefore, knee prostheses are implanted. While some patients recover quickly and forget on which knee they have had the surgery, others cannot escape from the pain, and need additional operations. Understanding the reasons for this will ultimately help to design better prostheses, and speed up the healing process. In addition, due to many reasons that merit investigation, prostheses last at most for only 15 years. With the necessary sensors added to these prostheses, the necessary data for understanding the reasons can be collected. This leads to the design of an electronic knee prosthesis. However, creating an electronic knee opens up many challenges. The SImOS project was started to examine feasibility and to reach the goal of building an electronic knee prosthesis. It is going to hold some force sensors to measure the forces in two condyles to achieve a better balance in the knee prosthesis. In addition, it is going to have magnetometers to understand the kinematics of the knee. All these factors increase the power consumption of the implanted electronics. However while remote powering is already an issue, further increasing the power consumption becomes more challenging. On the other hand, with the development of better tools, such as complex field solvers, it is easier to perform more complex analyses. This helps to review the already-used methods and propose better ones. To design the electronic knee, the problems related to the remote powering and communica- tion should be also solved. Inductive powering is an attractive solution for this kind of case and is already being used in biomedical applications. The small distance requirements between the external base station and the implantable medical devices and the fact that they are easily achievable with fairly small-sized antennas makes this method widespread. However, in some cases, the decision of the design parameters could be more challenging. If the distance is increased further, and metallic parts are added, the remote powering efficiency decreases drastically. As the subject of this thesis, a better approach to designing the remote powering coils is presented to overcome this problem and to achieve sufficiently high efficiency. This is done by showing that the s-parameter simulation or measurement results can be used directly to calculate the remote powering efficiency of the coil pairs. This allows us to use the result of the available field solvers directly to define an objective function. Since the objective function is easy to compute, by using an optimizer, which is chosen as simulated annealing in this thesis, it is shown that better coils can be designed. The achievable remote powering efficiency of the coil pair increases by designing the coil independently of the load. In this case, the optimal load of the coil would be different from the actual load. Hence the achievable efficiency cannot be reached. On the other hand, the actual load could be converted to the optimal load by using a matching network. This method is usually avoided due to the losses of the matching network elements especially the inductors. However, it is shown that the efficiency can be maintained nearly as it is by using only capacitors as the matching network elements in this design. It is also shown that it is possible to decouple the link design from the load by using a matching network so that the global remote powering efficiency is increased. In this case the performance of the coil pair only depends on the available volume and the distance in between. In addition, instead of using load shift keying for wireless communication, which is generally used for RFID tags, it is shown that building a stand-alone transmitter gives better results in terms of power consumption for high power-demanding applications. This thesis shows that the direct power consumption of a stand-alone transmitter could be less than the indirect power consumption that would occur in the case of load shift keying. By designing this transmitter the efficiency is maintained nearly as it is. All in all, 30% inductive link efficiency is achieved by using inductive powering for a distance of 2.5 cm. The coil at the implant is designed as an air-core rectangular solenoid and has dimensions of 18.2 mm x 2.8 mm x 3.9 mm. The proposed simulated annealing method is used for dimensioning the coil pair. With the designed microelectronic circuits in 0.18 μm technol- ogy, and the external class E-type power amplifier, 14% overall remote powering efficiency is obtained. 2.8V in addition to 1.8V operating voltage is provided by decoupling the link from the microelectronic design. With the designed switched-capacitor voltage doubler, the 2.8V supply is generated with an remote powering efficiency of 12%. For wireless bi-directional communication, a stand-alone transmitter is designed instead of the load shift keying. The FSK/OOK transmitter consumes 350 μW while transmitting at a rate of 57 kbps. For sending the commands to the implant, the power amplifier is designed as an ASK modulator. The required ASK demodulator at the implant can demodulate up to 1 Mbps of data-rate, while consuming only 15 μW.

EPFL2013

2D Material Based Inks For Room Temperature Printed Electronics

Sina Abdolhosseinzadeh

Functional printing is a versatile mass production method that has gained considerable scientific and industrial attention in the past few years. A wide range of electronics from passive circuit components (e.g., resistors and interconnects) to high-performance transistors and high-quality displays can now be printed energy-, resource-, and cost-efficiently. In spite of the recent progresses in the formulation of inks and significant reductions in their production costs, most of the commercially available inks are still very expensive (e.g., silver inks), and limited to a few conductive and insulator materials that usually require high-temperature thermal treatments to become fully functional. To enable new applications, and further reduce the production costs, it is necessary to develop novel inks based on semiconductive and new conductive materials (with improved chemical or optical properties) that can become functional after drying (dry-only inks). Development of such inks is very challenging, and the few successful results have been mostly obtained by polymer-based inks, which suffer from cost and chemical-stability issues.Since 2004 and after the first successful isolation of single-layer pristine graphene, 2D materials have disrupted almost all fields of science and technology, from medicine, to electronics and beyond. Their unique morphology, diverse and widely-tunable physical and chemical properties, ease of synthesis, low-cost of production, and abundance of raw materials have brought up new possibilities, which were not conceivable before. Formulation of additive-free inks for room-temperature printing of electronics is one of such possibilities. In spite of their great potential, formulation of additive-free 2D-material-based inks has so far been limited to low-concentration inks that are not suitable for high-throughput manufacturing, which is one of the main incentives for printing of electronics. Furthermore, current 2D materials' synthesis and processing methods have either low yield, or are not scalable, which further limit their real-world applications. Here in this work, several processing and ink formulation strategies are reported, which can address the aforementioned problems and pave the way towards out of lab application of 2D materials.In chapter 1, after a brief introduction on different device fabrication methods, basics of liquid-phase processing, especially the topics that are related to ink formulation and printing, are concisely reviewed. In chapter 2, a universal strategy for additive-free formulation of pristine 2D materials-based inks, and their scalable production are reported. Being a universal approach, this method allows us to print advanced electronic devices consisting different types of semiconductive and conductive materials. MXenes are a recently discovered group of 2D materials with exceptional optical and electronic properties which can revolutionize the printed electronics industry. Due to their importance and being at their early stages of discovery, 2 chapters of this thesis (chapters 3 & 4) have been dedicated to their ink formulation challenges. In chapter 3, the possibility of using byproducts of MXene synthesis as a sustainable ink formulation strategy has been investigated, which can simultaneously address the financial and environmental issues of printing electronics. In chapter 4, the conventional MXene ink formulation strategies are revisited to enable their scalable printing.

EPFL2021

SMD pressure and flow sensors for industrial compressed air in LTCC technology

Grégoire Boutinard Rouelle, Yannick Fournier, Thomas Maeder, Peter Ryser

In this work, we propose an SMD (surface mount device) pressure sensor in LTCC technology specially designed for standard industrial compressed air. It combines the measurement of pressure and temperature, with its integrated signal conditioning electronics for linearization, adjustment and temperature compensation. For the first time, such a sensor can be mounted on an integrated electro-fluidic platform like a standard component using surface mount technology, obviating the need for both wires and tubes. Manufacturing of the SMD sensor is described, as well as its performance and limitations. Furthermore, a proposal for an anemometric flow sensor is described. The heating / sensing elements of the sensor consist of PTC co- fired resistors suspended on bridges across the fluidic channel; different geometric and processing variants have been manufactured for tests. In the future, we intend to integrate this flow measurement function and corresponding electronics to the pressure sensor, resulting in an all-in-one integrated industrial compressed air flow –pressure – temperature sensor.