The status of magnetic bubble memories

Microelectronics and Reliability, Vol.18, pp. 191-192. Pergamon Press, 1978. Printed in Great Britain

THE STATUS OF MAGNETIC BUBBLE MEMORIES Dave Parratt Memories and Microprocessor Product Marketing Manager, Texas Instruments Ltd.

At one end of the spectrum of memory technology in digital computers semiconductor

currently used

and other data handling equipment,

random-access memories

are replacing ferrlte

core memories. 8oth provide fast data recovery at relatively high costs.

At the other end of the spectrum,

devices exploiting

magnetization,

as ferrite cores do, are virtually uncontested.

These devices,

drums,

discs,

and tapes provide inexpensive

storage at long recovery times by virtue of their mechanical nature. Magnetic bubbles - an emerging storage technique also offer storage by magnetization is non mechanical. used for bubbles industry.

and serial access.

The material

The access, however

and circuit processing

techniques

are similar to those in the semiconductor

Single crystal materials

that are easier to grow

than silicon, higher bit densities per unit area, levels without

data

alignment requirements

and fewer mask

in processing combine to

make the per bit memory cost very much lower than that typical for silicon integrated

memories

and indeed,

compare favourably with many mechanically devices.

Furthermore,

low enough to

accessed memory

bubbles have reliability that is high even

by solid-state device standards and offer economically access times that can substantially

a range of

close the current access gap

in the memory spectrum. Magnetic bubbles are mobile cylindrical domains that can be generated in a thin magnetic

layer and moved within the layer

by interaction with propagate paths processed directly onto the layer and magnetised by external fields.

The Storage

material can be either a magnetic garnet grown expitaxially on a non magnetic garnet substrate, magnetic

or an amorphous metallic

layer sputtered onto a subatrate such as glass.

Magnetic materials which support bubbles as small as 0.5 in diameters ace available promising storage densities of 10 8 bits /in 2.

~un

in excess

The arrival of the first commercially available magnetic bubble memory chip from Texas Instruments,

a 92,304-bit major-minor191

D. Parratt

192

loop d e v i c e h o u s e d in a d u a l - i n - l i n e p a c k a g e less than half a cubic inch in v o l u m e , easily

marks

a milestone

accessible nonvolatile

package,

it has e v e r y

magnetic

storage.

power,

and w i l l

d e n s i t y goes

in m e m o r y

memory

advantage

foreseen

It is s m a l l e r

Offering

for it o v e r m e c h n i c a l

and faster,

eventually become

up e n o u g h

evolution.

in a s e m i c o n d u c t o r - l i k e

cheaper,

consumes

as soon

and e n o u g h p r o d u c t i o n

less

as chip

experience

accumulates.

But

initial

storage

applications

for large

microcomputer are a l r e a d y

mass

s t o r a g e of at m o s t

systems,

storage

requires

Mor~-over, size

the

in small

or

advance

o[

92 - k i l o b i t in excess

lies

as the c e n t r a l

e]ectYonic:; ~;l:Ol-aqu and

of r e q u i r e m e n t s ,

and control

circuits,

storage undoubtedly

quite extensive

for microprocessor

its cost as low as possible, designed

unit

it is never n e c e s s a r y as can h a p p e n w i t h

which often account

makes

technology,

this circuitry

compatibility.

To keep

a family of large-scale-integrated

specifically

System cost will

for bubbles will be available

moved

further decrease

devices

into production,

a viable

solution

and further

in the future as larger support

cab]es

~'~]pat'Jt.y LI) I~P t a i l ~ l - ~ ' d

by the end of 1978.

bubble memory

in the

an{1 i n t + , r c ~ l H ~ e c i : i n q

for a large part of the entry cost of any storage magnetic-bubble

bubbles

processing

floppy discs.

As for interface

circuits

level,

s t o r a g e of both p r o g r a m s

But the real b e a u t y

increments,

in

For

over a s e p a r a t e m e c h a n i c a l

interface

but

At this

floppy discs.

the n o n - v o l a t i l e

b u h b l ~ " lU~lnol'y a l l o w : ;

purchase memory cassettes

small

r e s i d i n g on the same b o a r d

]otn

in mass

long been p r e d i c t e d ,

a few m e g a b i t s .

is a d e f i n a t e a d v a n t a g e .

unit - a s i g n i f i c a n t that

as has

cost-competitive with

microprocessor and data

of b u b b l e m e m o r i e s w i l l be not

computers,

components

such that the technology

are

will become

for more and more applications.

to

!<~