electrodes – part ii - polytechnique montréal · electrodes – part ii ... bonding pads silicon...

GBM8320 Dispositifs Médicaux Intelligents

Electrodes – Part II

Mohamad Sawan et al. Laboratoire de neurotechnologies Polystim !

!!

http://www.cours.polymtl.ca/gbm8320/[email protected]!

M5418!

April 2013

GBM5320 - Dispositifs Médicaux Intelligents GBM8320 - Dispositifs Médicaux Intelligents 2

Integrated Microelectrodes : Course outline •  Introduction

−  Electrogenic cell

•  Electrode/electrolyte interface −  Electrical double layer −  Half-cell potential −  Polarization −  Electrode equivalent circuits

•  Biopotential electrodes −  Body surface electrodes −  Internal electrodes −  Implantable electrodes −  Electrode arrays −  Microfabricated electrodes −  Microelectrodes.


Metal-plate electrodes Large surface: Ancient, therefore

still used, ECG • Metal disk with stainless

steel; platinum or gold coated • EMG, EEG • Smaller diameters • Motion artifacts • Disposable foam-pad: Cheap!

(a) Metal-plate electrode used for application to limbs. (b) Metal-disk electrode applied with surgical tape. (c) Disposable foam-pad electrodes, often used with ECG

Commonly used biopotential electrodes Body-surface electrodes •  Metal-plate ; •  Suction ; •  Floating ; •  Flexible.


Double-sided Adhesive-tape ring

Insulating package Metal disk

Electrolyte gel in recess

(a)‏ (b)‏

Reusable

(c)‏

Snap coated with Ag-AgCl External snap

Plastic cup

Tack

Plastic disk

Foam pad Capillary loops

Dead cellular material

Germinating layer

Gel-coated sponge Disposable

Commonly used biopotential electrodes Metal plate electrodes (Floating electrodes)

(a) Recessed electrode with hot structure;

(b) Cross-sectional view of electrode (a)

(c) Cross-sectional view of another disposable electrode.


•  Body contours are often irregular

•  Regularly shaped rigid electrodes may not always work

•  Special case : infants

•  Used materials - Polymer or nylon with silver - Carbon filled silicon rubber

(Mylar film).‏

(a) Carbon-filled silicone rubber electrode. (b) Flexible thin-film neonatal electrode. (c) Cross-sectional view of the thin-film electrode in (b)

Commonly used biopotential electrodes Flexible electrodes


•  Needle and wire electrodes for percutaneous measurement of biopotentials:

•  Insulated needle electrode

•  Coaxial needle electrode.

•  Bipolar coaxial electrode.

•  Fine-wire electrode connected to hypodermic needle, before being inserted.

•  Cross-sectional view of skin and muscle, showing coiled fine-wire electrode in place.

Internal Electrodes


Implantable electrodes

•  Electrodes for detecting fetal ECG (Use of intracutaneous needles)

•  Suction electrode

•  Helical electrode

•  Electrodes for Cardiac stimulation.

•  Electrodes for detecting biopotentials

•  Wire-loop electrode

•  Platinum-sphere cortical surface potential electrode

•  Multielement depth electrode.


Implantable neural electrodes

•  ENG measurement (three contacts) •  Stimulation (2 contacts)

•  Cuff electrodes

•  Helical electrodes •  Pins electrodes

•  Multicontacts electrodes •  etc


Microfabricated Electrode Arrays

•  Examples of microfabricated electrode arrays:

(a)  One-dimensional plunge electrode array (b)  Two-dimensional array, and (c)  Three-dimensional array.

(c)‏

Tines

Base

Exposed tip

Contacts Insulated leads

(b)‏

Base

Ag/AgCl electrodes

Ag/AgCl electrodes

Base Insulated leads

(a)‏

Contacts


Microelectrodes based on microelectronics

•  Beam-lead multiple electrodes : Wise, et al.

•  Multielectrode silicon probe : Drake et al.

•  Multiple-chamber

electrode : Prohaska et al.

•  Peripheral-nerve electrode : Edell.

(b)‏

(d)‏

(a)‏

(c)‏

Bonding pads

Silicon probe

Exposed electrodes

Insulated lead vias

Lead via

Electrode

Silicon probe

Miniature insulating chamber Hole

Channels Silicon chip

Contact metal film

Si substrate Exposed tips

SiO2 insulated Au probes

Various applications


Microelectrodes based on microelectronics

An 8-probe array of 64 contacts each


Microelectrodes Micromachining

Robofil 2030

Metalic arrays of electrodes

• Wire-EDM cut • Surface electropolish • Oxalic acid attack • Platinum deposition • Epoxy base • Support Grinding • Assembly.


• Surface electropolish • Oxalic acid attack • Platinum deposition • Epoxy base • Support Grinding • Assembly.

Microelectrodes Micromachining


Structure of a metal microelectrode for intracellular recordings.

Structures of two supported metal microelectrodes: (a) Metal-filled glass micropipet (b) Glass micropipet or probe, coated with metal film.

Microelectrodes Intracellular recordings : The glass micropipet


•  The electrical activity of cells can be recorded without disrupting the cell membrane using extracellular recording techniques

•  For extracellular recordings, the cells are located directly on top of a transducing element, which is, in most cases, either a metallic electrode or an open-gate transistor

•  When electrical activity or a so-called action potential in a cell occurs, ions flow across the cell membrane within msec.

•  Ions sensitive transistors can be used to transduce the cells activity.

Microelectrodes Extracellular recordings (in vivo)


Extracellular Recording (in vivo)

•  When a cell is close to a transducer, the moving ions generate an electric field or voltage, which can be recorded by the metallic microelectrode or field-effect transistor

•  Extracellular recordings are non-invasive (no puncturing of the cell membrane)

•  Models: - Metal electrode - Open field-effect transistor.


Why use IC and CMOS technology

•  Two main advantages in using integrated-circuit (IC) or CMOS technology: –  Connectivity: larger numbers of transducers or electrodes can be

addressed by on-chip multiplexing architectures

–  Signal quality; the signal is conditioned right at the electrode by means of dedicated circuitry units (filters, amplifiers)

•  The use of CMOS technology allows to realize a large number of electrodes on a small system chip

•  On-chip microelectronics, as provided by the use of IC or CMOS technology, translate into system capability: signal conditioning can be performed on-chip, ensuring that weak neural signals are faithfully recorded;

Summary



•  A CMOS system also enables a bidirectional communication via the electrodes (stimulation and recording);

•  Smart switching schemes allow for stimulating the cell ensemble via an arbitrarily selectable set of electrodes, all while recording from other electrodes uninterruptedly during stimulation

•  On-chip analog-to-digital conversion means that such chip produces a robust signal that may be easily manipulated and transferred without compromising its information content

•  Moreover, the use of on-chip electronics allows for the monolithic integration of the complete system on a single chip, which leads to small system dimensions and low power consumption, a key requirement for implantable devices

Summary (Cont’d)



•  The use of multiplexers enables the integration of a large number of electrodes or transducers so that measurements at high spatiotemporal resolution become feasible

•  Traditional Microelectrode arrays (MEAs) without multiplexers usually offer 64 electrodes with each electrode needing a connection to external circuitry, which adds parasitic capacitance and attenuates the weak signals

•  CMOS-based MEAs comprise up to 16,384 electrodes and the needed addressing circuitry on the same chip

•  A disadvantage of CMOS ICs is that silicon is not transparent to visible light in contrast to standard cell culture substrates used in biology

Summary (Cont’d)


IC and CMOS technology: The drawbacks

•  The IC or its components can corrode upon operation and long-term exposure to liquids (salt water)

•  A good packaging solution is needed: –  To protect the IC against metabolism products

–  To prevent the cells from being poisoned or disturbed by toxic materials released by the IC, such as the CMOS metal aluminum that dissolves in saline solution.

Notes : •  Make a better electrode •  Research different electrode technologies

–  Ion selective, immunosensors, ISFET, electrochemical –  MEMS microelectrode technologies –  Polymer based electrodes..

Summary (Cont’d)

electrodes – part ii - polytechnique montréal · electrodes – part ii ... bonding pads silicon...

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