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Chip Scale Review March • April • 2019

[ChipScaleReview.com]

Packaging of bioimplantable electronics

By P. Markondeya Raj

[Florida International University]

,

Nithin Nedumthakady, Rao Tummala

[Georgia Institute of Technology]

ioimplantable electronics

interface with the human body

to extract precise medical

data and generate and affect biological

functions by providing electrical stimuli.

The term “implantable” indicates that the

device is intended to be totally or partially

introduced, surgically or medically, into

the human body and remain there for an

extended period. These electronics have

numerous applications, including sensing

and monitoring of physiological conditions,

therapy for chronic diseases and disorders,

functioning as artificial organs, and

enabling prostheses of limbs to replace lost

functions in the body.

Packaging technologies are becoming

critical to achieve the next generation in

integration, functionality, miniaturization,

and long-term reliability and operability

of implantable bioelectronic systems. Such

systems represent true heterogeneous

integration because power, radio frequency

(RF), analog and digital functions are

integrated in 3D and ultra-miniaturized

form factors in hermetic and biocompatible

packages with elect rode ar rays and

interfaces that directly interact with the

human body. Implantable electronics

should seamlessly integrate high-density

elect ronic sub -systems with multi-

terminal electrode arrays on f lexible

substrates with biocompatible materials,

while achieving power delivery through

efficient power transfer, conversion, and

storage. In addition, these systems must

operate reliably in aqueous media over an

extended time. Several major innovations

that combine high-density feedthroughs,

i nt eg r at ed magnet ic and capacit or

components, advanced biocompatible

polyme r and met al elect rode s and

interfaces, and embedded or fan-out

packaging in flexible substrates aim to

create new breakthroughs in this area.

Implantable/bioelectronics

I mp l a n t a b l e o r b i o e l e c t r o n i c s

comprise three fundamental elements:

a) an electronics hub that receives and

processes power and data

and sends control signals

to b) the electrode array,

which transmits the control

signals or receive s t he

recorded signals and sends

to the signal amplifier in

the electronics hub, and c)

hermetic and biocompatible

c a s e s o r l a y e r s t h a t

protect the system from

its environment. A cross

s e c t i o n o f a g e n e r i c

bioelectronic package is

shown i n

Figure 1

and

described in more detail.

3D e l e c t ron i c s hub.

Bioele c t r on ic s r equ i r e

heterogeneous integration of

several functions including:

power transfer and conversion, data

processing, controller for power delivery

to the neural interfaces, and analog-to-

digital controllers with signal amplification

and conversion. Such systems need to

provide sensing, analog, and digital

functions to process signal, power, and

data telemetry functions from an external

unit while maintaining compatibility with

the environment and functioning reliably.

These requirements need to be achieved

withi n millimeter dimensions. The

electronics hub is 3D-integrated in ultra-

thin packages with the highest component

densities to meet the application needs.

This central electronic unit is encased in

3D-integrated, miniaturized, hermetic

packages using high-density electrical

interconnections in and out of the package

wit hout compromisi ng hermet icit y

and biocompatibility.

The key function of the electronics

hub is power and data reception and

c onve r s ion . T he p owe r t el eme t r y

subsystem is made up of two parts: the

antenna and the rectifier (also referred to

as a rectenna). The antenna receives the

RF energy that is rectified to DC power

and stored within a capacitor or used to

charge a battery. To have the greatest

efficacy, a rectenna must be designed

for high-performance energy reception

and compatibility with the transmitting

antenna. The key requi rements are

efficient power conversion with new

t opolog ie s , b e t t e r de sig ne d pu l s e

duty cycle, high-Q components, and

integration of actives and passives on a

hermetic, flexible system on a package.

The efficiency of a rectifier is heavily

influenced by the required power density

and rectenna array configurations.

Flexible electrode arrays.

The hub

is hermetically packaged and interfaced

with electrode arrays, preferably with

remateable connections for removal and

replacement in a surgical environment.

The electrode arrays are made to be

chemically inert and reliable in the body.

The electronic hub package is directly

terminated with high-density electrode

arrays that interface with neurons. The

electrode system needs to be f lexible

to conform to the shape of the organs

and withstand large stresses. The f lex

electrode array connector, created using

biocompatible dielectrics and electrodes,

is used to accomplish this.

B i o c omp a t i b l e a n d h e r me t i c

packaging for long-term reliability.

Bioelect ronics have high liabilities

B

Figure 1:

(top) Simplified schematic representation of an emerging 3D

bioelectronic package; and b) (bottom) Processing hub integrated with a

flexible electrode array.