Implantable biomimetic microelectronic systems design.

In this article, design examples will be presented for a biomimetic microelectronic system for a retinal prosthesis that electrically stimulates the retinal neurons. The system replaces the functionality of vision in blind patients affected by retinitis pigmentosa and age-related macular degeneration. The components and signal processing needed for a cortical prosthesis are described. Integration of all the components of a wireless biomimetic microelectronic system, such as input signal conditioning, power telemetry, data telemetry, stimulation amplifier and control circuitry (microstimulator), and a neural recording and processing device, into a single chip or a package is a tremendous challenge, requiring innovative approaches at both circuit and system levels and consideration of the multiple trade-offs between size, power consumption, flexibility in functionality, and reliability of the microelectronics. The chips described in this paper are prototypes for testing their implemented functionalities. The die sizes do not reflect the actual size of the implant. When the microelectronics are finally integrated, the circuits will be optimized to minimize the area. The use of submicron CMOS technology will also help reduce the die area. It should be noted that the biocompatible package encapsulating the electronics will increase the implant size.     

A power‐efficient current‐mode neural/muscular stimulator design for peripheral nerve prosthesis

This paper presents a 16‐channel power‐efficient neural/muscular stimulation integrated circuit for peripheral nerve prosthesis. First, the theoretical analysis is presented to show the power efficiency optimization in a stimulator. Moreover, a continuous‐time, biphasic exponential‐current‐waveform generation circuit is designed based on Taylor series approximation and implemented in the proposed stimulation chip to optimize the power efficiency. In the 16‐channel stimulator chip design, each channel of the stimulator consists of a current copier, an exponential current generator, an active charge‐balancing circuit, and a 24‐V output stage. Stimulation amplitude, pulse width, and frequency can be set and adjusted through an external field‐programmable gate array by sending serial commands. Finally, the proposed stimulator chip has been fabricated in a 0.18‐μm advanced complementary metal‐oxide‐semiconductor process with 24‐V laterally diffused metal oxide semiconductor option. The maximum stimulation power efficiency of 95.9% is achieved at the output stage with an electrode model of 10‐kΩ resistance and 100‐nF capacitance. Animal experiment results further demonstrate the power efficiency improvement and effectiveness of the stimulator.     

Active Microelectronic Neurosensor Arrays for Implantable Brain Communication Interfaces

We have built a wireless implantable microelectronic device for transmitting cortical signals transcutaneously. The device is aimed at interfacing a cortical microelectrode array to an external computer for neural control applications. Our implantable microsystem enables 16-channel broadband neural recording in a nonhuman primate brain by converting these signals to a digital stream of infrared light pulses for transmission through the skin. The implantable unit employs a flexible polymer substrate onto which we have integrated ultra-low power amplification with analog multiplexing, an analog-to-digital converter, a low power digital controller chip, and infrared telemetry. The scalable 16-channel microsystem can employ any of several modalities of power supply, including radio frequency by induction, or infrared light via photovoltaic conversion. As of the time of this report, the implant has been tested as a subchronic unit in nonhuman primates (${sim} 1$ month), yielding robust spike and broadband neural data on all available channels.      

Balance prostheses for postural control

There is a clear need for a prosthesis that improves postural stability in the balance impaired. Such a device would be used as a temporary aid during recovery from ablative inner-ear surgery and as a permanent prosthesis for those elderly prone to falls. Research using a one-axis device that estimates body tilt and displays it to vestibulopathic subjects via an array of tactile vibrators has demonstrated feasibility. The noninvasive, vibrotactile display of body tilt helped the balance-impaired subjects to reduce their body sway during standardized tests. The motion sensor array is comprised of three MEMS linear accelerometers and three MEMS rate gyros whose sensitive axes are aligned along three orthogonal directions to provide six-degree-of-freedom (dof) motion information.     

On the Thermal Elevation of a 60-Electrode Epiretinal Prosthesis for the Blind

In this paper, the thermal elevation in the human body due to the operation of a dual-unit epiretinal prosthesis to restore partial vision to the blind affected by irreversible retinal degeneration is presented. An accurate computational model of a 60-electrode device dissipating 97 mW power, currently under clinical trials is developed and positioned in a 0.25 mm resolution, heterogeneous model of the human head to resemble actual conditions of operation of the prosthesis. A novel simple finite difference scheme combining the explicit and the alternating-direction implicit (ADI) method has been developed and validated with existing methods. Simulation speed improvement up to 11 times was obtained for the the head model considered in this work with very good accuracy. Using this method, solutions of the bioheat equation were obtained for different placements of the implant. Comparison with in-vivo experimental measurements showed good agreement.      

Cortical neural prosthesis performance improves when eye position is monitored.

Neural prostheses that extract signals directly from cortical neurons have recently become feasible as assistive technologies for tetraplegic individuals. Significant effort toward improving the performance of these systems is now warranted. A simple technique that can improve prosthesis performance is to account for the direction of gaze in the operation of the prosthesis. This proposal stems from recent discoveries that the direction of gaze influences neural activity in several areas that are commonly targeted for electrode implantation in neural prosthetics. Here, we first demonstrate that neural prosthesis performance does improve when eye position is taken into account. We then show that eye position can be estimated directly from neural activity, and thus performance gains can be realized even without a device that tracks eye position.     

A Stackable Bonding-Free Flextensional Piezoelectric Actuator

A flextensional actuator was designed using commercial multilayer stacked actuator so as to produce large displacements at intermediate force levels. The simple design chosen eliminated the need for bonding the actuators into the frame and permitted easy series connection of multiple units. To satisfy the need for a fiber grating tuning device to interrogate an array of Bragg grating fiber optic stress sensors, a tuning device using four series connected units was constructed. The unit performs well, but the actual measured amplification is less than theoretical expectation. The problem was traced to unwanted flexing of the simple original frame and a hinged more robust flexing beam construction was shown to eliminate the problem.     

A Stackable Bonding-Free Flextensional Piezoelectric Actuator

A flextensional actuator was designed using commercial multilayer stacked actuator so as to produce large displacements at intermediate force levels. The simple design chosen eliminated the need for bonding the actuators into the frame and permitted easy series connection of multiple units. To satisfy the need for a fiber grating tuning device to interrogate an array of Bragg grating fiber optic stress sensors, a tuning device using four series connected units was constructed. The unit performs well, but the actual measured amplification is less than theoretical expectation. The problem was traced to unwanted flexing of the simple original frame and a hinged more robust flexing beam construction was shown to eliminate the problem.     

A biomimetic retinal stimulating array.

A retinal prosthesis capable of restoring face recognition, reading, and mobility to blind patients is within the capability of microsystems technology. Electrode arrays can be made dense enough to be able to place thousands of pixels into the macula. Electrode materials can supply safe and effective stimulus current. This review examines some prior work in electrical stimulation of the retina and simulations of phosphene-based vision as a basis to produce design constraints for a biomimetic retinal-stimulating array. An array is designed considering the needs of the end users (blind individuals), the biology of diseased retina, and the limits of electrode technology. Other technology to support the system such as high-density stimulus generation circuitry and hermetic packaging face significant challenges but solutions can likely be realized to some degree.     

Perceptual thresholds and electrode impedance in three retinal prosthesis subjects.

Three test subjects blind from retinitis pigmentosa were implanted with retinal prostheses as part of a FDA-approved clinical trial. The implant consisted of an extraocular unit that contained electronics for wireless data, power, and generation of stimulus current, and an intraocular unit that consisted of 16 platinum stimulating electrodes arranged in a 4 x 4 pattern within a silicone rubber substrate. The array was held to the retina by a small tack. The stimulator was connected to the array by a multiwire cable and was controlled by a computer based external system that allowed precise control over each electrode. Perception thresholds and electrode impedance were obtained on each electrode from the subjects over several months of testing. The electrode distance from the retina was determined from optical coherence tomography imaging of the array and retina. Across all subjects, average thresholds ranged from 24-702 microA (1-ms pulse). The data show that proximity to the retina played a role in determining the threshold and impedance, but only for electrodes that were greater than 0.5 mm from the retina.     

Implantable transducer for two-degree of freedom joint angle sensing.

An implantable joint angle transducer (IJAT) was developed to provide command-control and feedback-control information for chronic use with functional neuromuscular stimulation (FNS) neuroprostheses. The IJAT uses Hall effect sensors to transduce joint angle. A titanium encapsulated array of Hall effect sensors and support circuitry is surgically implanted in one bone, and a similarly encapsulated permanent magnet in an opposing bone, across a joint. The IJAT provides consistent, reliable, high quality signals that reflect joint movement from midsized two-degree-of-freedom joints. IJAT's were implanted using a chronic in vivo dog model to demonstrate the feasibility of implantation and periodic measurement techniques, and to validate modeling techniques used for prediction of function and calibration. The flexion resolution ranged from 0.4 to 3.0 degrees over a range of 115 degrees. The maximum deviation from a linear response was 9 degrees. The resolution and linearity depend on several transducer and joint geometry parameters, and can be predicted prior to implantation and calibrated after implantation. The results of this study 1) defined the most appropriate hermetic capsule designs for the IJAT sensor and magnet, 2) defined the best orientation of the magnetic field to optimize device function, 3) provided a computer model of the IJAT to aid in placement, calibration, and evaluation of the device, 4) verified the surgical techniques used to implant the device, and 5) verified the long-term functionality and the biocompatibility of the device.     

玻璃包覆层对钴基非晶丝巨磁阻抗效应的影响

分别用机械法和HF酸化学腐蚀方法去除金属芯丝直径为13μm、总直径为47μm的钴基Co68.15Fe4.35Nb1Si11.5B15.0非晶态玻璃包覆丝的玻璃包覆层,发现HF酸腐蚀去除玻璃层比机械法处理过的非晶丝的巨磁阻抗磁场灵敏度要高,HF酸剥离的非晶裸丝的巨磁阻抗最大磁场灵敏度可达ξ=105.02%/(79.6A/m)。HF酸去除玻璃包覆层的微细丝的阻抗效应要比有玻璃包覆层的丝在更低的外部磁场作用下达到巨磁阻抗比的最大值,在频率为f=4.07MHz、磁场强度为Hdc=176A/m处,非晶裸丝的磁阻抗效应达到最大值113.6%,其巨磁阻抗效应的磁场灵敏度ξ=42.9%/(79.6A/m)。     

Mathematical Modeling and Analysis of MEMS Deformable Mirror Actuated by Electrostatic Piston Array

In this report, we constructed a simple mathematical analysis model for a new MEMS deformable mirror using an electrostatic piston array. The deformable mirror has been developed as a wavefront compensation device in adaptive optics for retinal observation. The device realizes a large convex deformation with a low operation voltage because of moving bottom electrodes on the pistons. The constructed model is based on the plate theory and simple superposition of the actuation components. The calculated deformation analyzed using this model agrees well with that analyzed using the finite element method not only in deformation shape but the peak‐valley deformations. In addition, the calculation time is much shorter, so the model can be used for design optimization of the device.     

DEVICE DESIGN FOR THE NOVEL HANDWRITING RECOGNITION SYSTEM

ABSTRACT

A microelectromechanical systems-based handwriting system device was designed. We proposed an ominidirectional acoustical sensor microarray which can offer isotropic directional sensitivity with a high radiation acoustic power when it as a transmitter and a high array spatial gain (AG) when it as a receiver. It has been designed for use in the novel handwriting recognition system to attain a large writeable scale and to write in any direction. The proposed array device based on novel ferroelectric thin film has excellent performance, miniature size and high reliability, and could be fabricated with conventional integrated circuit process.     

Development of a chipscale integrated microelectrode/microelectronic device for brain implantable neuroengineering applications

An ultralow power analog CMOS chip and a silicon based microelectrode array have been fully integrated to a microminiaturized "neuroport" for brain implantable neuroengineering applications. The CMOS integrated circuit (IC) includes preamplifier and multiplexing circuitry, and a hybrid flip-chip bonding technique was developed to fabricate a functional, encapsulated microminiaturized neuroprobe device. Our neuroport has been evaluated using various methods, including pseudospike detection and local excitation measurement, and showed suitable characteristics for recording neural activities. As a proof-of-concept demonstration, we have measured local field potentials from thalamocortical brain slices of rats, suggesting that the new neuroport can form a prime platform for the development of a microminiaturized neural interface to the brain in a single implantable unit. An alternative power delivery scheme using photovoltaic power converter, and an encapsulation strategy for chronic implantation are also discussed.     

A miniaturized neuroprosthesis suitable for implantation into the brain

This paper presents current research on a miniaturized neuroprosthesis suitable for implantation into the brain. The prosthesis is a heterogeneous integration of a 100-element microelectromechanical system (MEMS) electrode array, front-end complementary metal-oxide-semiconductor (CMOS) integrated circuit for neural signal preamplification, filtering, multiplexing and analog-to-digital conversion, and a second CMOS integrated circuit for wireless transmission of neural data and conditioning of wireless power. The prosthesis is intended for applications where neural signals are processed and decoded to permit the control of artificial or paralyzed limbs. This research, if successful, will allow implantation of the electronics into the brain, or subcutaneously on the skull, and eliminate all external signal and power wiring. The neuroprosthetic system design has strict size and power constraints with each of the front-end preamplifier channels fitting within the 400 /spl times/ 400-/spl mu/m pitch of the 100-element MEMS electrode array and power dissipation resulting in less than a 1/spl deg/C temperature rise for the surrounding brain tissue. We describe the measured performance of initial micropower low-noise CMOS preamplifiers for the neuroprosthetic.     

Digital implementation of biologically inspired Wilson model,population behavior,and learning

Spiking neurons, as a computational unit, are the main part in biological information processing systems. This paper presents a digital hardware implementation of a biological neuron on a field‐programmable gate array due to its high accuracy and high speed, especially for large‐scale simulations which is a key objective in the neuromorphic research field. Although this is a computationally expensive task, the use of more biological realistic system results in higher accuracy in mimicking biological behaviors of neural networks. Given that, the Wilson model is one of the most important biological neuron models that can be used in the architecture of spiking neural networks. To be closer to biological systems, a method is proposed to test the possibility of implementation of the Wilson neuron model on digital platforms. The results of the hardware implementation of the Wilson neuron and a spiking network on a field‐programmable gate array, capable of character recognition with supervised learning algorithm, are presented in this paper; moreover, population behavior of this model is simulated. In large‐scale implementation of 2000 Wilson neuron model, population capability, feasibility, and costs are investigated. This paper presents a method to the implementation of Wilson neurons on digital platforms, suggesting that the available system is an attainable platform for the implementation of large‐scale biologically plausible neural networks on field‐programmable gate array devices. Hardware synthesis, physical implementation on field‐programmable gate array, and theoretical analysis confirm that the proposed model has hardware so that makes it an appropriate model for the large‐scale digital implementation.     

Design of a Ferroelectric Programmable Logic Gate Array

A programmable logic gate array has been designed utilizing ferroelectric field effect transistors. The design has only a small number of gates, but this could be scaled up to a more useful size. Using FFETs in a logic array gives several advantages. First, it allows real-time programmability to the array to give high speed reconfiguration. It also allows the array to be configured nearly an unlimited number of times, unlike a FLASH FPGA. Finally, the Ferroelectric Programmable Logic Gate Array (FPLGA) can be implemented using a smaller number of transistors because of the inherent logic characteristics of an FFET. The devices were only designed and modeled using Spice models of the circuit, including the FFET. The actual device was not produced. The designs consist of a small array of logic gates. Other gates could easily be produced. They are linked by FFETs that control the logic flow. Timing and logic tables have been produced showing the array can produce a variety of logic combinations at a real time usable speed. This device could be a prototype for a device that could be put into imbedded systems that need the high speed of hardware implementation of logic and the complexity to need to change the logic algorithm. Because of the non-volatile nature of the FFET, it would also be useful in situations that needed to program a logic array once and use it repeatedly after the power has been shut off.     

Microelectronic packaging for retinal prostheses.

An innovative parylene-based high-density chip-level integrated interconnect (CL-I/sup 2/) packaging system for retinal implants id discussed. The implications of this CL-I/sup 2/ technology for retinal prosthesis packaging effort are far-reaching. This technology obviates the need for a technician to create electrical and mechanical connections one by one. Instead, the technology is limited only by standard photolithography and standard microfabrication techniques, providing the capability for a reduction of an order of magnitude or more in the center-to-center pad distances that can be accommodated in the process. High-density electrode arrays are thereby feasible, because the fabrication process places no limit on the number of output pads that can reasonably be connected to the array.