Ming-Yuan Cheng

A Monolithically Integrated Pressure/Oxygen/Temperature Sensing SoC for Multimodality Intracranial Neuromonitoring

A fully integrated SoC for multimodality intracranial neuromonitoring is presented in this paper. Three sensors including a capacitive MEMS pressure sensor, an electrochemical oxygen sensor and a solid-state temperature sensor are integrated together in a single chip with their respective interface circuits. Chopper stabilization and dynamic element matching techniques are applied in sensor interface circuits to reduce circuit noise and offset. On-chip calibration is implemented for each sensor to compensate process variations. Measured sensitivity of the pressure, oxygen, and temperature sensors are 18.6 aF/mmHg, 194 pA/mmHg, and 2 mV/°C, respectively. Implemented in 0.18 m CMOS, the SoC occupies an area of 1.4 mm × 4 mm and consumes 166 μW DC power. A prototype catheter for intracranial pressure (ICP) monitoring has been implemented and the performance has been verified with ex vivo experiment.

3D probe array integrated with a front-end 100-channel neural recording ASIC

Brain–machine interface technology can improve the lives of spinal cord injury victims and amputees. A neural interface system, consisting of a 3D probe array and a custom low-power (1 mW) 100-channel (100-ch) neural recording application-specific integrated circuit (ASIC), was designed and implemented to monitor neural activity. In this study, a microassembly 3D probe array method using a novel lead transfer technique was proposed to overcome the bonding plane mismatch encountered during orthogonal assembly. The proposed lead transfer technique can be completed using standard micromachining and packaging processes. The ASIC can be stacking-integrated with the probe array, minimizing the form factor of the assembled module. To minimize trauma to brain cells, the profile of the integrated probe array was controlled within 730 μm. The average impedance of the assembled probe was approximately 0.55 MΩ at 1 kHz. To verify the functionality of the integrated neural probe array, bench-top signal acquisitions were performed and discussed.

Biopackaging of Intracranial Pressure Microsystem for Multimodality Neuro Monitoring of Severe Head Injury Patients

In this work, we present the biopackaging and integration method of an intracranial pressure microsystem for multimodal neural monitoring. The neural monitoring chip used is a System-on-Chip (SoC) which has Microelectromechanical Systems (MEMS) capacitive pressure sensor that is fabricated in-house after Complementary Metal-Oxide Semiconductor (CMOS) wafer fabrication process, with a temperature sensor and an oxygen sensor in order to achieve multimodal neural monitoring functions. Polyimide is used for the substrate of the SoC die and passive component due to its biocompatibility and flexibility. A reversed stand-off stitch wire bonding process was employed in order to achieve a low-profile wire looping for the interconnection of the SoC die to the substrate. The biocompatible coatings of this implantable system consist of Parylene-C (for covering temperature and pressure sensors), Nafion® (for covering oxygen sensor), and medical grade silicone elastomer (for overall device encapsulation). The ICP microsystem wireless reader module was packaged in a customized biocompatible hermetic Teflon housing. To reinforce and seal the catheter, which is integrated with the microsystem, during the device implantation into the brain tissue, it is filled until the wire bonded portion with polydimethylsiloxane. Similarly, the guiding tip of the catheter which will facilitate the sensor device to penetrate into the brain tissue is made and casted from a specially designed mold using polydimethylsiloxane as the material. Verification of the packaging feasibility was measured by measuring the sensitivities of the pressure sensor, oxygen sensor, and temperature sensor. The whole microsystem also passed the ISO 10993-5 standards in vitro cytotoxicity test with a conclusion of no reactivity and no cell lysis cell growth in cell culture, verifying its biocompatibility

Evaluation of biodegradable coating on the stiffness control of the polyimide-based probe used in neural devices

In this work, an assembled and integrated flexible probe array with biodegradable coating for stiffness control is demonstrated. The proposed method will help to overcome the stiffness issue faced by polymeric probe array during insertion into the brain tissue. It is proposed to do coating with biodegradable material to increase the stiffness of the probe shanks. Assembly process is simplified as polymer probe and cable were being monolithically fabricated, only the connector needs to be soldered onto the bonding pads. To enhance the soldering between connector and bonding pads, rigid stiffener is designed at the bonding pads region to provide robust support for soldering process and for insertion process.

Biopackaging of Minimally Invasive Ultrasound Assisted Clot Lysis Device for Stroke Treatment

The biopackaging of a minimally invasive sonothrombolysis device (ultrasound-assisted clot lysis device) for acute stroke treatment is proposed and presented. Instead of using thrombolytic medicine (tissue plasminogen activators) in combination with the ultrasound wave for total blood clot dissolution, the proposed sonothrombolysis device uses only pure ultrasound wave generated from Microelectromechanical Systems (MEMS)-based piezoelectric micromachined ultrasonic transducers (pMUTs) that were designed and fabricated in-house. The proposed biopackaging aims to simplify and shorten the clot lysis procedure which could help speed up the recanalization or surgical removal of the blood clots in acute ischemic stroke treatment. The device packaging is composed of two main integrated parts – the three-dimensional (3D) printed United States Pharmacopeia (USP) Class VI plastic material and the 50-µm thin polyimide flexible printed circuit board (PI FPCB) substrate. The 3D printed USP Class VI plastic material is configured as the drainage catheter of the dissolved clots as well as the custom-fit carrier of the PI FPCB substrate that is coupled and secured onto it. A single layer PI FPCB is used as the substrate of either two or four number of MEMS-based pMUTs, which are attached on it using biocompatible epoxy and wire bonded using 1 mil gold wire. The PI FPCB is also designed such that it is directly compatible with the Flat Flex Cable (FFC) connector of the external circuitry that would trigger the MEMS-based pMUTs to generate acoustic signals as well as measure the viscosity of the blood clot. To drain the dissolved blood clots, the catheter is printed with a number of holes are placed across and around the pMUT location. The catheter tip is rounded-off to remove sharp corners from the plastic material. Buckling analysis is done to simulate stiffness of the catheter when inserted into the brain tissue leading to the center of blood clot. The buckling load of the 3D printed USP Class VI plastic material at a total deformation of 0 – 1 mm at 1 sec is 2038.4N as compared to the buckling load of the silicone rubber (usual catheter material, without the metal guiding rod) which is only 0.128N. The simulation results showed that the 3D printed USP Class VI plastic material will not buckle easily during penetration in the brain tissues or insertion into the blood clot compared to silicone rubber. In order to validate that the combination of materials used in sonothrombolysis device are non-reactive and are not cytotoxic, in vitro cytotoxicity test based on ISO 10993-5 standards is performed. The materials passed.

Simulation Analysis of a Conformal Patch Sensor for Skin Tension and Swelling Detection

Intravenous cannulation (IV) has a potential medical complication known as extravasation which arise when the fluid accumulates in the subcutaneous tissue layer causing skin swelling symptom. The cost incurred for the addition hospitalization stay and treatment due to the extravasation complication is high. The current detection devices for extravasation is expensive, bulky and it is not suitable for the daily routine IV cannulation administration. In this work, a wearable and conformal sensor patch was developed for detection of skin swelling and tension. Structural simulation analysis and ex-vivo characterization of thin film metal (Ti/Cu/Au: 20 nm/ 2 µm /20 nm) were performed and result were presented in the paper. The sensor patch was able to detect skin tension and swelling of less than 3mm deformation height caused by 2-ml of fluid infusion. The sensitivity of the electrode sensor was 45% change of resistance per ml volume of infused solution.

Forward Tactile Sensing Device Development and Biopackaging for Endovasular Guidewire Intervention Application

Revascularization procedure for peripheral artery disease is dependent on surgeons skill and experience for a successful procedure. An integrated sensor on guidewire is proposed to reduce such dependency during the procedure. The development and packaging of the sensor with a hybrid-silicone-polymer substrate (HSPS) and a silicon stopper arepresented in this paper. A compact HSPS (0.4mm x 10mm x0.31mm) with trace width/spacing of 20μm/20μm for five output signals and Si stopper with safety displacement feature to prevent force overloading are fabricated. It is able to enhanced current sensor integrated guidewire by improving the robustness and provides a forward sensing mechanism (orthogonal assembly). The assembled device is able to measure up till 42mN force with a resolution of 0.2mN. Detail of characterization testing and result will be presented in the paper.

Characterization of CMOS electrochemical oxygen sensor for biomedicai applications

This paper presents the characterization procedures of a CMOS electrochemical oxygen sensor and its readout circuits in application specific integrated circuit (ASIC) format. As the sensor needs to be tested inside deionized water, a master controller Printed Circuit Board (PCB) is designed to provide power and control signals to test the ASIC. The transimpedance (TIA) amplifier gain, voltage amplifier gain, sensor array sensitivity and 8-bit Digital-to-Analog Converter (DAC) trimming voltage are configured through the master controller. The oxygen sensor ASIC is mounted on another PCB with chip-on-board (COB) packaging. Biocompatible hydrogel Nafion is coated to cover the entire sensor electrodes for oxygen transportation. The measured sensor sensitivity is 0.78 mV/mmHg and a transient output voltage change of 50 mV is observed when the deionized water is changed from air saturation to nitrogen saturation.

Ultra slim packaging and assembly method for 360-μm diameter guide wires

In this work, we present an ultra-slim profile packaging and assembly solution of a 360-μm diameter medical guide wire fitted and integrated with silicon based fractional flow reserve (FFR) sensor. The miniaturization of the whole sensorized guide wire assembly without sacrificing its sensing functionality was made possible by the use of polyimide flexible printed circuit board (FPCB) as the substrate material for the silicon platform and by the use of lowest possible wire looping profile to create interconnection between the FFR sensor and the FPCBs bonding pads using the gold wires. In order to reinforce and protect the wire interfaces, as well as to maintain the required biocompatibility of the whole system, a thin layer of Polydimethylsiloxane (PDMS) was used for the encapsulation process. Long signal wires were then attached to the bonding pads of FPCB before finally fitted inside a miniaturized metal housing. This whole system has easily fit and integrated with the 360-μm diameter medical guide wire. In order to verify the packaging feasibility, the electrical short testing of the bonding pads and SEM observations were conducted.

Silicon cap structure development and microassembly for forward tactile sensing in endovascular guidewire intervention

Guidewire procedure for peripheral artery disease treatment is heavily dependent on the surgeons skills and experiences. In order to reduce such dependency, sensor-enhanced forward sensing guidewire is proposed. In this paper, we proposed a silicon cap structure that increases the robustness and efficient force transfer of the existing sensor-enhanced forward sensing guidewire. Silicon cap structure of 0.32 × 0.32 × 0.40mm has been fabricated using two masks process. Assembly of silicon structure with sensor having a 30μm overloading protection limit and resistance changes of 25kΩ with applied force ranging from 0∼40mN has been demonstrated.