Packaging and Ceramic Feedthroughs for the Boston Retinal Prosthesis

Transcription

1 Packaging and Ceramic Feedthroughs for the Boston Retinal Prosthesis Tom Salzer Hermetric, Inc. Doug Shire Veterans Health Administration W. Kinzy Jones Florida International University Ali Karbasi Florida International University

2 Other Collaborators and Vendors COLLABORATORS Tom Salzer William Drohan, MS Patrick Doyle, MS Jinghua Chen, MD, PhD Marcus Gingerich, PhD Oscar Mendoza Joseph Rizzo, MD John Wyatt, PhD VENDORS Hermetric, Inc. Valtronic Technologies Morgan Advanced Ceramics Sonny Behan Consulting Cirtec Analog Circuit Works..and many more 4/4/2014 The Boston Retinal Implant Project 2

3 Presentation Outline Fundamentals of Visual Prosthetics Retinal Implant System Design ASIC Design Overview Communication System Summary Feedthrough Fabrication Video Processing Methods Summary April 4, 2014 The Boston Retinal Implant Project 3

4 Boston Visual Prosthesis: Definition An electronic implantable device to restore functional vision to patients with certain forms of blindness, primarily retinal degenerative diseases.

5 Degenerative Retinal Diseases Age-related Macular Degeneration (AMD) Loss of photoreceptors in macula (center), working outward Strikes at age with increasing incidence May take decades to go blind 2 million cases in US, tens of millions worldwide

6 Degenerative Retinal Diseases II Retinitis Pigmentosa (RP) Loss of photoreceptors in periphery, working inward Genetic, strikes at age Typically a decade or less to go blind 100,000 cases in US, 1.7M worldwide

7 How Visual Prostheses Work A visual prosthesis stimulates nerves in the visual system based on an image from an external camera. The patient should see a pixelated, scoreboard-style image corresponding to the scene in their environment.

8 System Overview Images are captured by the external camera and processed by a handheld computer Image data and power are wirelessly transmitted to the implant using a 6.78 MHz RF carrier frequency 4/4/2014 The Boston Retinal Implant Project 8

9 Challenges for Visual Prostheses Surgical Place electrode array safely and securely Place electronics in bio-compatible location Microfabrication Electrode materials that can safely deliver needed charge but not physically damage tissue Hermetic packaging of electronics Hundreds of channels needed to create detailed images Electrical Engineering Deliver balanced electrical current to electrodes Wirelessly deliver power and image data to implant

10 What We Learned from First Human Trials The concept works patients can see spots and lines, and distinguish from controls in which no stimuli were applied. We needed to develop a wireless, chronic implant to allow patients to adapt to this new form of input over time.

11 Sub-Retinal Implant Electrode array enters the space under the retina from the back, through the scleral wall of the eye.

12 Current Generation Prosthesis Hundreds of channels (>256) Smaller hermetic case New Application- Specific IC Chip and Multi-Layered, SiCencapsulated Electrode Array

13 Device Design: Concept Flat Ti Case Faces Orbit Header Faces Sclera Flexible Multi-Electrode Array April 4, 2014 The Boston Retinal Implant Project 13

14 Chip Overview The ASIC we have designed receives image data and delivers stimulation currents to the retinal nerves Chip is 5mm x 5mm and low-power (0.1mW standby, about 30% efficiency when stimulating) and will not significantly heat the eye Portion of Die Showing Current Drivers And 1.8V Digital Logic April 4, 2014 The Boston Retinal Implant Project 14

15 Wireless Components: Summary April 4, 2014 The Boston Retinal Implant Project 15

16 Image Acquisition and Processing Upper Figure shows image transformation using Boston system and live video, which is zoomed, threshold filtered, and then down-sampled Filter Selections include Blurring, Edge Extraction, Thresholding, Contrast Enhancement, Zoom In, Rotate Image, and Linear (e.g., low-pass) Lower down-sampling Figure is from literature Utility of high-density prosthesis is clear! 4/4/2014 The Boston Retinal Implant Project 16

17 Image Acquisition and Processing II Images 30 frames/sec & sent to external controller Saved in memory as 640 x 480 grayscale (7-bit) images Subsequently sent through a series of user-defined filters, chosen e.g. from: contrast enhancement, edge extraction, blurring, and thresholding After filtering, images are down-sampled to >256 points, one for each electrode We achieve frame rates from 5 to 20 frames/sec, depending on task Camera s automatic gain control compensates for varying ambient light levels Algorithm depends on patient input, and task lighting, and/or clinician input Currently implemented on a personal computer running C++/ OpenCV Fitting or adjustment of image processing algorithms (and stimulation parameters, within safe limits) will be determined iteratively w/ patient input Portable version will run algorithms using a dedicated DSP system 4/4/2014 The Boston Retinal Implant Project 17

18 Package Assembly Pre-Molded Glued On Polyurethane Header Lip on Top Clamshell Assures Alignment Case Bottom Prepared for Projection Welding to Ferrule Upper and Lower Clamshell Halves Laser Welded Shut High Temperature Co-Fired Ceramic Disk with Signal Feedthroughs, Brazed to Titanium Ferrule April 4, 2014 The Boston Retinal Implant Project 18

19 Package Assembly II Co-fired ceramic feed-throughs have 256+ holes punched for individual stimulation sites Holes are filled with bio-compatible conductive material, fired, and brazed to the 11mm diameter Ti case Hermeticity measured by helium leak rate: 1x10E-09 to 1x10E-08 standard cc/sec April 4, 2014 The Boston Retinal Implant Project 19

20 Cofired Platinum /Alumina Feedthroughs The interaction of punched alumina substrates and Pt via metallizations upon firing were evaluated for the: Effect of particle size Effect of firing atmosphere Effect of alloying additives Effect of binder burn-out Effect of alumina / glass composition A robust materials and processing system was developed to allow air firing of feedthrough discs over a range of alumina compositions ( % alumina), that meet the hermeticity standard for medical implant devices 4/4/2014 The Boston Retinal Implant Project 20

21 Materials Analysis and Characterization Room temperature and high temperature X-ray diffraction Thermal analysis (DSC, TGA, dilatometry) Hermeticity testing (to 1 X 10 E(-9) std cc He/sec) Particle Analysis (BET, morphology) High Resolution Transmission electron microscopy (HREM) HREM Micrograph of Edge of Fired Via showing Void-free Alumina Pt Interface 4/4/2014 The Boston Retinal Implant Project 21

22 Internal Assembly of Device Solder paste is screened over the grid of the interior surface of the conductive feedthroughs The paste is melted to create solder bumps The bumps are mated with a matching pattern on the internal circuit board and the assembly is reflowed in an oven 4/4/2014 The Boston Retinal Implant Project 22

23 External Assembly of Device Electroplated Gold contacts are formed on the proximal end of the 256+ channel multi-electrode arrays The feedthroughs in the fired ceramic discs are similarly electro-plated with Gold The two parts are joined to one another using thermosonic bonding at 125 degrees C April 4, 2014 The Boston Retinal Implant Project 23

24 Discussion