Electrical Feedthroughs Research Articles

Laser fabrication of electrical feedthroughs in polymer encapsulations for active implantable medical devices

Hermetic electrical feedthroughs are essential for safe and functional active implantable biomedical devices and for a wide range of other applications such as batteries, supercapacitors, OLEDs and solar cells. Ceramics and metals have previously been the materials of choice for encapsulations, while polymers have advantages of ease of mass production and end user compatibility. We demonstrate a laser sealing technology that gives hermetic, mechanically strong feedthroughs with low electrical resistance in a polyetheretherketone (PEEK) encapsulation. The conductive pathways are wires and sputtered thin films. The water vapor transmission rate through the fabricated encapsulations is comparable to that of PEEK itself.

A Force Rebalanced Micro-Gyroscope Driven by Voltages Oscillating at Half of Structure’s Resonant Frequency

This paper demonstrates a simple and cost-effective approach to separate the mechanical vibration signals from the electrical feedthrough signals resulted from stray capacitances, which is a generic issue in capacitive MEMS gyroscopes. Taking advantage of the quadratic relationship between the drive voltage and the electrostatic force, the micro-structure can be driven into resonance by using voltages oscillating at half of its resonant frequency. As a result, the mechanical signals and the electrical feedthrough can be readily identified in the frequency domain. Although the forcer in this control scheme is nonlinear, it is still possible to adopt this method to implement a force rebalance loop. A particular feedback controller is designed to achieve a linear measurement. Meanwhile, we simplify the modulation and demodulation processes in the feedback loop to obtain a fully linear system design. In addition, the noise characteristic is analytically investigated by using power spectral density in the open-loop case, and is numerically simulated in the closed-loop case. The experimental results not only demonstrate the feasibility of the control scheme, but also show that the fabricated micro-gyroscope using the proposed approach exhibits moderate performances. The nonlinearity of the scale factor is 290 ppm within the measurement range of ±300 deg/s. The bias instability achieves about 4.5 deg/h with an angular random walk of 11.9 deg/h/sqrt(Hz).

Vacuum cavity encapsulation for response time shortening in flexible thermal flow sensor

A vacuum cavity encapsulation fabrication process for a thermal sensor based on a Cu on polyimide (COP) substrate was studied to shorten the response time, and it was applied to a flow sensor application. First, the sacrificial etching properties of a Cu layer for designing and forming a cavity under a heater for thermal isolation and an electrical feedthrough into the Cu layer were evaluated. The etching rates depended on the hole size of an etching mask pattern and the distance between two holes. Then, the relationship between the amount of parylene dimer and the sealing thickness in a lateral direction in the etching hole by its deposition was investigated to encapsulate the cavity under a vacuum condition. The thickness increased linearly with the amount of dimer, and the hole was successfully sealed by the parylene film under a vacuum condition. The vacuum cavity encapsulation was applied to the flexible thermal flow sensor to shorten the response time. The response time value was successfully shortened to three-fifths by applying the vacuum cavity encapsulation, and it did not change after 2 months.

Capacitive Feedthroughs for Medical Implants.

Important technological advances in the last decades paved the road to a great success story for electrically stimulating medical implants, including cochlear implants or implants for deep brain stimulation. However, there are still many challenges in reducing side effects and improving functionality and comfort for the patient. Two of the main challenges are the wish for smaller implants on one hand, and the demand for more stimulation channels on the other hand. But these two aims lead to a conflict of interests. This paper presents a novel design for an electrical feedthrough, the so called capacitive feedthrough, which allows both reducing the size, and increasing the number of included channels. Capacitive feedthroughs combine the functionality of a coupling capacitor and an electrical feedthrough within one and the same structure. The paper also discusses the progress and the challenges of the first produced demonstrators. The concept bears a high potential in improving current feedthrough technology, and could be applied on all kinds of electrical medical implants, even if its implementation might be challenging.

Elastic airtight container for the compaction of air-sensitive materials.

We report on the design and fabrication of a simple and versatile elastic canister for the compaction and hot-pressing of air-sensitive materials. This device consists of a heated double-ended floating die assembly, enclosed in a compressible stainless steel bellows that allows the action of an external hydraulic press in a uniaxial motion. The enclosure is fitted with vacuum, gas, and electrical feedthroughs to allow for atmosphere control, heating, and in situ process monitoring. The overall chamber is compact enough to be portable and transferrable into and out of a standard laboratory glovebox, thus eliminating the problem of exposing samples to ambient atmosphere during loading and unloading. Our design has been tested up to 600 °C and 7500 kg-force applied load, conditions within which transparent ceramics of anhydrous halides can be produced.

外径70 mm のコンフラットフランジにマウントした簡易金属蒸着源の製作

We have constructed a simple metal evaporator mounted on a conflat flange with an outer diameter of 70 mm. It consists of a tungsten filament, an alumina tube, two molybdenum electrodes, tantalum foils, and electric feedthroughs. Evaporation rates are measured as a function of electric current. We used it to prepare an Au thin film and a Si (111)-√3 ×√3 R30°-Au surface.

Implantable diamond capsules for electro stimulation and recording

Event Abstract Back to Event Implantable diamond capsules for electro stimulation and recording Kumaravelu Ganesan1, 2, David J. Garrett1, Nick Opie2 and Steven Prawer1 1 University of Melbourne, School of Physics, Australia 2 SmartStent PTY LTD, Australia Introduction: Implantable electronic devices must necessarily adhere to a very strict set of standards before they can be approved for clinical use. One of these standards is the requirement that electronically active components such as microprocessors must be encapsulated hermetically to protect the body from the toxicity of conventional electronic components and as well as to protect the components from the harsh environment inside the body which leads to accelerated device failure. This article provides an overview of an all-diamond hermetic capsule for retinal as well as cortical implants for electrostimulation and recording. Materials and Methods: Diamond Microelectrode array: Diamond microelectrode array of 3-D surface electrodes as shown in fig1a and fig 1.b was fabricated using conventional as well as unconventional fabrication techniques. The microelectrodes are nitrogen incorporated unltrananocrystalline diamond and the body is polycrystalline diamond[1]. CMOS chip integration: Lithographically defined Indium bumps and flip chip bonding technique was used to bond the CMOS processor to the electrode to make one-to-one connection. Electrical feedthrough: An active braze alloy of 95% gold was brazed in vacuum environment to form the electrical feedthrough, electrical contacts as well as the braze line for final laser welding. Laser Microwelding : Pulsed Laser welding technique was used to join the two halves together hermetically. Fig. 1. (a) Components of the diamond/gold encapsulation with high-density diamond electrode array (2) flip-chip bonded to a 256 channel stimulator application specific integrated circuit (ASIC) (1) and a diamond box with integrated feedthroughs for power and data transfer (3). The two diamond components are sealed by welding around the outer edges of the braze seam (b).[2] (c)Diamond cortical implant for recording. This is approximately half the size of the retinal implant shown in (b) and has the dimension of 2X0.7X0.3mm. A receiver Rx coil in fabricated on the diamond body. Results and Discussion: An all diamond 256 channel retinal implant was fabricated and tested successfully. A cortical recording implant is under development with the wireless power and data transfer facilities. Conclusion: A new hermetic encapsulation paradigm for a medical implant , using polycrystalline diamond, was presented. The new packaging technology uses high-conductivity gold braze feedthroughs for power and data input and a laser welded seam of Gold-ABA braze joining the diamond shell components. This work was funded in part from Australian Research Council through its Special Research Initiative (SRI) in Bionic Vision Science and Technology grant to Bionic Vision Australia (BVA); ARC Linkage grant 2015(SMARTSTENT PTY LTD)

Isolation Resistance of Encapsulated Electrical Conductors and Terminations for Biomedical Applications

Implanted electronic medical devices are evolving into architectures that are comprised of multiple packages that require reliable, high density electrical interconnections. Both power and digital signals must be routed between devices on cables that are immersed in an ionic, electrically conductive medium. Electronics are typically housed in hermetic packages with electrical feed throughs that must also be protected from the implant environment. The polymer materials used to encapsulate cable conductors and terminations must be biocompatible, compliant and of minimal thickness. These requirements result in materials that are susceptible to ion diffusion and migration in electric fields. We have used finite element models to explore the effects of geometries, electric field intensity and material properties on the time dependent electrical isolation resistance of cables and terminations. Simple beaker tests have been used to evaluate the isolation resistance of samples under bias as a function of time to validate our finite element models.

Electrodeposition of Nanowires and Nanostructures from Supercritical Fluids

Supercritical fluids are potentially highly attractive media for the electrodeposition of metals and semiconductors into complex nanostructures [1]. Supercritical fluids readily penetrate porous and nanoporous structures because they have essentially zero surface tension. They also have low viscosities and hence show enhanced mass transport rates. Depending on the choice of electrolyte and solvent they can also have a wide electrochemical window. However these advantages do not come without several disadvantages; their generally low dielectric constants, and the necessity to work in sealed systems at elevated temperature and pressure. For these reasons the field of electrodeposition from supercritical fluids is still relatively unexplored with very little published work on electrodeposition from single phase supercritical systems. In order to explore the possibilities of using electrodeposition from supercritical fluids to make sub 20 nm nanostructures and nanostructured devices we have focused on the electrodeposition of a range of p-block elements (Ga, In, Ge, Sn, Pb, Sb, Bi, Se and Te) from supercritical difluoromethane [2]. In this lecture I will present results of our latest results on electrodeposition of these elements from supercritical difluoromenthane, the characterization of the electrodeposited materials, and work on the electrodeposition of sub-20 nm nanowires. I will discuss the experimental systems and novel reagents required to undertake this work, including the development of a simple high pressure, high temperature electrical feedthrough. I will also discuss our progress towards making transistors from supercritical fluid electrodeposited nanowires. Acknowledgements:This is a contribution from the SCFED Project (www.scfed.net), a multidisciplinary collaboration between the Universities of Southampton, Nottingham and Warwick and is funded by a Program Grant from EPSRC (EP/I033394/1).

First boundary electrical feedthroughs for the heating neutral beams injectors of ITER

The first boundary feedthroughs of the ITER heating neutral beam (HNB) injectors are key components of the neutral beam system. They allow the penetration of signals and power from/to the beam line components (BLC) and front end components (FEC), through the confinement boundary of ITER.The design status of the two types of feedthroughs is presented in the first part. This includes the design requirements, cabling strategy, the analysis done and the maintenance strategies. The second part deals with the qualification of the feedthroughs. Being made of brittle material and not covered by mechanical standard a qualification by testing strategy is proposed based on existing rules and norms.The design of the feedthroughs is almost finished and satisfies all the requirements. The next step is the procurement for their integration in the MITICA [1] test bed and the detailed definition of the qualification tests to be carried out for the HNB feedthroughs.

CO Adsorption/Desorption Studies on Thin Platinum Films By Electrical Resistance Measurements

Platinum (Pt) is a widely used catalyst for numerous chemical and electrochemical processes. Nanosize Pt particles supported on high surface area carbon are used as both cathode and anode in proton exchange membrane fuel cells (PEMFC) [1]. It is well known that even with 25 ppm CO in the H2 fuels can degrade the performance of a typical PEMFC [2]. Many studies have been reported on the mechanism of CO poisoning on Pt surface using techniques such as LEED, ELS, IRRAS, FYNES, etc. [3,4]. Most of these experiments were done under UHV (~10-10 torr) and low temperatures (~150K) using Pt single crystals. We report here studies on CO adsorption/desorption using electrical resistance measurements. The experiments were conducted in a test chamber consisted of a silica glass cylinder clamped between two metallic plates with O-rings to ensure gas-tight seals. An electrical heater and a sample holder were inserted into the chamber. A thermocouple was introduced into the chamber to measure the sample temperature. Electrical feed-throughs were inserted from the end plates into the chamber. Also connected to the end plates were gas inlet/outlet fittings. A gas supply system consisting of flow meters and valves was used to introduce various atmospheres into the chamber. Resistance measurements were conducted using digital multimeters. Data acquisition was done using LabView software. Figure 1 shows the measured resistance response from the Pt film upon switching gases between 10% H2 in Ar and 100 ppm CO in Ar at ~60oC. The temperature versus time profile is also included in the figure. Clear evidence of increasing film resistance during CO adsorption and decreasing film resistance during CO desorption was observed. Similar experiments were conducted at various temperatures and CO partial pressures. By correlating the resistance change with CO surface coverage of Pt atoms and the Langmuir model, we observed that for the desorption process, a plot of ln(1-R0/R) or ln(ΔR/R) vs. t is linear, where R and R0 are respectively the resistance for the film at a given time and the initial stage (equilibrated under 10% H2 in Ar). The absolute value of the slope gives the value of desorption rate constant, kd . The adsorption stage was studied by plotting dR/(Rdt) vs. R. The intercept of such a plot gives kapco+kd, where ka is the adsorption rate constant and pco is the CO partial pressure under testing. Since kd has been obtained by the desorption process, ka can be determined with known pco . Figure 2 shows examples of linear plots from both adsorption and desorption stages. It is seen that the desorption stage can be described by a single rate constant, kd . The plot dR/(Rdt) vs. R , however, is not linear. The adsorption stage cannot be thus described a single rate constant, kapco. The dR/(Rdt) vs. R plots, however, could be described by a two stage process. The initial stage can be described by a relatively high value of , and probably corresponds to adsorption on high energy sites (possibly surface steps). The later stage can be described by a relatively low value of , which possibly corresponds to adsorption on flat surfaces. The AFM images (not shown here) show the film surface was quite rough indicating the presence of surface steps and kinks. The present studies show that kinetics and mechanism of gas adsorption on very thin metal films can be studied by measuring electrical resistance. Supported by the National Science Foundation under Grant Number CBET 0931080 and the US Department of Energy under Grant Number DE-FG02-06ER46086.

Hermetic diamond capsules for biomedical implants enabled by gold active braze alloys

As the field of biomedical implants matures the functionality of implants is rapidly increasing. In the field of neural prostheses this is particularly apparent as researchers strive to build devices that interact with highly complex neural systems such as vision, hearing, touch and movement. A retinal implant, for example, is a highly complex device and the surgery, training and rehabilitation requirements involved in deploying such devices are extensive. Ideally, such devices will be implanted only once and will continue to function effectively for the lifetime of the patient. The first and most pivotal factor that determines device longevity is the encapsulation that separates the sensitive electronics of the device from the biological environment. This paper describes the realisation of a free standing device encapsulation made from diamond, the most impervious, long lasting and biochemically inert material known. A process of laser micro-machining and brazing is described detailing the fabrication of hermetic electrical feedthroughs and laser weldable seams using a 96.4% gold active braze alloy, another material renowned for biochemical longevity. Accelerated ageing of the braze alloy, feedthroughs and hermetic capsules yielded no evidence of corrosion and no loss of hermeticity. Samples of the gold braze implanted for 15 weeks, in vivo, caused minimal histopathological reaction and results were comparable to those obtained from medical grade silicone controls. The work described represents a first account of a free standing, fully functional hermetic diamond encapsulation for biomedical implants, enabled by gold active alloy brazing and laser micro-machining.

Hermetic Electrical Feedthroughs Based on the Diffusion of Platinum into Silicon

Within this paper a novel approach for the development of hermetic electrical feedthroughs is introduced. So far, every vertical feedthrough induces at the feedthroughs' interfaces possible paths for water to leak across the hermetic barrier into the hermetic package. The presented approach is based on the diffusion of platinum into silicon, locally changing the electrical behavior of the substrate due to the induced impurities. This method avoids destroying the bulk material, in this case silicon, preserving the hermetic barrier environment. Different n-type silicon substrates were investigated for their usability through various diffusion experiments under two gas atmospheres: Argon/hydrogen and pure nitrogen. A significant change in silicon behavior could be shown for one of the used substrates. The current flowing through the bulk could be decreased by a factor of around 12 for an argon/hydrogen atmosphere and by around 10 for pure nitrogen. The current directly correlates with a local increase of the substrates' resistance, demonstrating the possibility of adapting the electrical properties of a substrate to create insulating areas within a conductive substrate.

MEMS Wafer‐Level Packaging Technology Using LTCC Wafer

SUMMARYThis paper describes a versatile and reliable wafer‐level hermetic packaging technology using an anodically bondable low‐temperature co‐fired ceramic (LTCC) wafer, in which multilayer electrical feedthroughs can be embedded. The LTCC wafer allows many kinds of microelectromechanical systems (MEMS) to be more flexibly designed and more easily packaged. The hermeticity of vacuum‐sealed cavities was confirmed after 3000 cycles of thermal shock (–40 30 min/+125 30 min) by the diaphragm method. To practically apply the LTCC wafer to a variety of MEMS, the electrical connection between the MEMS on a Si wafer and feedthroughs in the LTCC should be established by a simple and reliable method. We have developed a new electrical connection method: the electrical connection is established by porous Au bumps, which are part of the Au vias exposed in wet‐etched cavities on the LTCC wafer. A 100% yield of both electrical connection and hermetic sealing was demonstrated. A thermal shock test up to 3000 cycles confirmed the reliability of this packaging technology.

Triple stack glass-to-glass anodic bonding for optogalvanic spectroscopy cells with electrical feedthroughs

We demonstrate the use of an anodic bonding technique for building a vacuum tight vapor cell for the use of Rydberg spectroscopy of alkali atoms with thin film electrodes on the inside of the cell. The cell is fabricated by simultaneous triple stack glass-to-glass anodic bonding at 300 °C. This glue-free, low temperature sealing technique provides the opportunity to include thin film electric feedthroughs. The pressure broadening is only limited by the vapor pressure of rubidium and the lifetime is at least four months with operating temperatures up to 230 °C.

Theoretical Analysis and Experimental Quantification of the Gas Leakage Due to Electrical Feedthroughs in Anodic Bonding

In this paper, theoretical analysis and experimental quantification of the gas leakage issue due to feedthroughs in anodic bonding are presented. The theoretical analysis was conducted to quantitatively analyze the influence of metal feedthroughs in anodic bonding on the package quality based on the plate elastic deformation theory and the theory of gas flow in capillaries. To validate the analysis, absolute capacitive pressure sensors were fabricated with gold feedthroughs in the silicon–glass bonding interface. The dimensions of the leakage microchannels due to feedthroughs were quantified experimentally and the leakage rate following the anodic bonding was measured using a helium leak detector. The deviations from calculated values were less than 30% in different channel dimensions and 38.3% in leakage rates between theoretical analysis and experimental studies. To address this issue, a new structure was designed, fabricated and characterized where localized Si–Au eutectic bonding was used to improve the package quality. By fine tuning two key parameters of bonding temperature and feedthrough step height, the new design was demonstrated to improve the hermetic levels by at least two orders of magnitude compared to the conventional design without eutectic bonding.

Continuous flow, explosives vapor generator and sensor chamber.

A novel liquid injection vapor generator (LIVG) is demonstrated that is amenable to low vapor pressure explosives, 2,4,6-trinitrotoluene and hexahydro-1,3,5-trinitro-1,3,5-triazine. The LIVG operates in a continuous manner, providing a constant and stable vapor output over a period of days and whose concentration can be extended over as much as three orders of magnitude. In addition, a large test atmosphere chamber attached to the LIVG is described, which enables the generation of a stable test atmosphere with controllable humidity and temperature. The size of the chamber allows for the complete insertion of testing instruments or arrays of materials into a uniform test atmosphere, and various electrical feedthroughs, insertion ports, and sealed doors permit simple and effective access to the sample chamber and its vapor.

Wafer-level hermetic MEMS packaging by anodic bonding and its reliability issues

This paper reviews wafer-level hermetic packaging technology using anodic bonding from several reliability points of view. First, reliability risk factors of high temperature, high voltage and electrochemical O2 generation during anodic bonding are discussed. Next, electrical interconnections through a hermetic package, i.e. electrical feedthrough, is discussed. The reliability of both hermetic sealing and electrical feedthrough must be simultaneously satisfied. In the last part of this paper, a new wafer-level MEMS packaging material, anodically-bondable low temperature cofired ceramic (LTCC) wafer, is introduced, and its reliability data on hermetic sealing, electrical interconnection and flip-chip mounting on a printed circuit board (PCB) are described.

The Study of the Inductive Coil to the Acoustic Performance of Electromagnetic Driven Microspeaker

Electromagnetic driven MEMS speakers using Polydimethylsiloxane (PDMS) membrane have been investigated to obtain a better sound pressure level (SPL) respond in low frequency regime. The comparison between measure and COMSOL simulation of fabricated microspeakers shows that the copper coil and its electrical feedthrough have a strong effect on the rigidity of the membrane thus on the SPL. Without considering the feedthrough effect, wide bandwidth starting at low frequency can be obtained while the coil is placed in the centre of the membrane, whereas placing the coil close to the membrane border instead will give a better response in low frequency with feedthrough effect

An all-diamond, hermetic electrical feedthrough array for a retinal prosthesis

The interface between medical implants and the human nervous system is rapidly becoming more and more complex. This rise in complexity is driving the need for increasing numbers of densely packed electrical feedthrough to carry signals to and from implanted devices. This is particularly crucial in the field of neural prosthesis where high resolution stimulating or recording arrays near peripheral nerves or in the brain could dramatically improve the performance of these devices. Here we describe a flexible strategy for implementing high density, high count arrays of hermetic electrical feedthroughs by forming conducting nitrogen doped nanocrystalline diamond channels within an insulating polycrystalline diamond substrate. A unique feature of these arrays is that the feedthroughs can themselves be used as stimulating electrodes for neural tissue. Our particular application is such a feedthrough, designed as a component of a retinal implant to restore vision to the blind. The hermeticity of the feedthroughs means that the array can also form part of an implantable capsule which can interface directly with internal electronic chips. The hermeticity of the array is demonstrated by helium leak tests and electrical and electrochemical characterisation of the feedthroughs is described. The nitrogen doped nanocrystalline diamond forming the electrical feedthroughs is shown to be non-cyctotoxic. New fabrication strategies, such as the one described here, combined with the exceptional biostability of diamond can be exploited to generate a range of biomedical implants that last for the lifetime of the user without fear of degradation.