June 30, 2025 • 15 mins
U.S. National Science Foundation-supported researchers are developing a new class of semiconductors with great potential for next-generation microelectronic devices. Zetian Mi, a professor at the University of Michigan, discusses his group's work with wurtzite ferroelectric nitride semiconductors.
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Episode Transcript
Available transcripts are automatically generated. Complete accuracy is not guaranteed.
(00:03):
This is the Discovery Files podcastfrom the U.S.
National Science Foundation.
Semiconductors are the backboneof most modern electronic devices,
from smartphones and home appliancesto MRI scanners and satellites.
Breakthroughs in semiconductorsand microelectronics
will be key to overcoming limitsin critical areas, including artificial
(00:23):
intelligence, quantum computing,manufacturing and communications.
We're joined by Zetian Mi,
professor of electrical engineeringand computer science
at the University of Michigan.
His group is working on a new classof semiconductors
with great potential for next generationmicroelectronic devices.
Professor Mi,thanks so much for joining me today.
Thank you very much Nate.
It is my great honor and pleasureto have this opportunity to talk to you.
(00:46):
So I need to ask you about wurtziteferroelectric nitrites.
What is this?
So my group is working on three nitridesemiconductors.
This is materialthat's commonly used in our daily lives.
For example,we use this material for LED lighting.
They are also in our cell phonesand literally everywhere.
(01:09):
And the second most producedsemiconductors on this planet
next only to silicon.
So this material has been around, but for decades.
This materialis known to be piezoelectric.
Let me briefly explain what piezoelectric is.
So this material has fixedthe polarization inside of the material.
(01:33):
And, when you apply electric field,you can generate a string and vice versa.
So they can also be used as sensors.
So the ferroelectric
is a subset of the piezoelectric family.
By saying ferroelectricwe mean the electrical polarization
in the materialcan be reversed back and forth.
(01:56):
When we apply an external electric field.
Ferroelectric is not new, first discovered
around 100 years ago, 1920by a graduate student
when he was doing PhDat University of Minnesota.
But for nearly 100 years, the ferroelectric materials
are mostly oxide based.
Oxide based feroelectricthey have been used almost everywhere.
(02:20):
For example, in sensors, in industrysettings, in medical devices,
in ultrasonic.
However, the oxide ferroelectricalso has some fundamental limitations.
For examble,they are not stable in harsh environments.
It’s very difficultto make them compatible with a mainstream
semiconductor processing, and thereforelimit some of their applications.
(02:45):
And here we have one of the most producedsemiconductor material.
And now we can turn it into ferroelectric.
You can imagine the enormous opportunitiesthis can open.
And that'swhat we are really excited about.
So how do you store informationinside an electric field?
So electric field in the semiconductor
(03:08):
can have positive or negative directions.
Which means we can switchthe direction back
and forth for ferroelectric material
and then give us the opportunityto store the information.
For examplewe can define a positive direction
polarization as the information one,a negative as zero right.
(03:31):
Then we can store the information.
We can electrically reversethe polarization,
which means we can writeor reset the information in the material.
Or we can read the materialby applying a electrical signal.
We can read the information stored inside.
The most beautiful part ofthis is the information is stored there
(03:54):
without applying any external bias.
So once you set the polarization, there,
it will stay therewithout supplying any external power.
So this is a so-called nonvolatilememory device.
And so imagine if we can build
atomic scale memory cellswith a very little power consumption,
(04:17):
and we can integrate billions or trillionsof them on a very small size chip.
And that's going to really revolutionize
computingcommunication in the years to come.
So what is the benefit of lowerpower consumption with semiconductors?
Computing communication is consumingenormous amount power as we speak.
(04:40):
And with the AIthis is going to grow exponentially.
So how to reduce the power consumptionat the device level will be very critical.
Now let's first talk about this,this device power consumption.
There are many factors that will affectthe device power consumption.
For example, for memory device. Right.
(05:00):
How much powerwe need to reset or right to the signal,
how much power we need to useto read the signal, or how much power
we need to use to store the informationto maintain the information.
So what's really great about thismaterial is nonvolatile.
We do not need to have extra powerto maintain the information.
(05:24):
Now come back to the power consumptiondue to the writing
or reading for a memory device or,other devices.
It directly related to the efficiencyand also relate to the device size.
And for the wurtziteferroelectric nitrides.
Nowadays we can grow them atomic layerby atomic layer
(05:45):
so we can make them very, very small.
And therefore the power consumptioncan be drastically reduced
together with very high integrationdensity billions,
billions of devices can be integratedon a very small size chip.
What is the unique polarization capabilityin this material?
Yes. I'm glad you asked.
So for the wurtzite ferroelectric?
(06:08):
There have been interest and studies bymany research groups but for a long time.
There is a fundamental questionis for this wurtzite ferroelectric.
Once we switch the polarizationthen we have all the this
polarization within the same material,just like a bar magnet right.
(06:29):
The north and south pole.
When you try to put them together withinone material, how can they be stabilized?
And specificallyin the wurtzite ferroelectric?
When we switch the polarization
only part of the material,the polarization is switched.
So there will be domainsof different polarization.
(06:52):
At the interface, we may have two positiveelectric field facing each other.
How can this be stabilized.
This has remained a fundamental question.
So that's one of the studiesthat we recently published.
We showed that.
And and this dummy interface,
we have a new atomic scene structure
(07:14):
and this atomic structure different
from the host materialand has unbonded electrons,
which can stabilize the polarizationdiscontinuity.
Not only that, this electron density
is much higher than thatin the traditional gallium
nitride transistors,that this is like 100 times higher.
(07:38):
So provides future opportunities to design
nanoscale device with better performance.
How is this discoverygoing to really impact
the next generation of semiconductorsthat people see in their devices.
It’s going to impactin several different ways.
Gallium nitride devices are alreadyin many business sectors, right?
(08:03):
Almost in our daily lives.
And now we have this ferroelectricity
and it can enhance the performance
functionality of existing devices.
For example, it can make our cell phoneto have stronger, signal
less noise to operate more efficiently,
and secondly, it also broadensthe scope of the traditional oxide
(08:29):
ferroelectric beyondwhat can possibly be done.
Oxideferroelectric is a wonderful material.
However, this material has some challengeswhen operating in harsh environment.
For example in aerospace,
or spacecraft, in electrical vehicleswhere you often
(08:49):
have very high temperatureor other extreme conditions.
These wurtzite ferroelectric nitrides
are known to be very stableat very high temperature.
Up to 1000 degree Celsius.
That can have immediatelyimportant applications.
And also this wurtziteferroelectric nitrides can be grown
(09:11):
or synthesizeatomic layer by atomic layer.
And you can really scale these to verysmall size and with excellent performance.
So that will helpto make electronic devices
with better performancewith high integration density.
And also these material can be integratedwith the mainstream
(09:33):
electronics silicon and gallium nitridewhich will all enhance
the functionality of our futuremicroelectronics.
The exact scope and impact remainsto be seen, but,
many colleagues in academia,in the industry, we are very excited
with the enormous potentialof this new class of semiconductors.
(09:56):
Are there challengesgetting buy in from industry partners
when you develop a new materialor a new strategy
to introduce these materials into devicesthat they are currently producing?
Yes. As you correctly mentioned,for any new material,
there are important considerationshow they are going to be adopted
(10:18):
by the industry, how this is going to beintegrated with their production lines.
Some materialsmay have wonderful properties,
but if they cannot be adopted by industry,
they will only remainas a subject of research interest.
Very fortunately,for this material family.
It is based on an existing material,gellium nitride
(10:41):
is the secondmost produced semiconductor in industry,
and we only add 1or 2 elements into this material.
And then we can transform this material
to how wonderful propertiesnot existing before.
As a matter of fact,this material has already been
adopted in our next generationcell phones.
(11:04):
And we'll see more of those in the future.
I want to ask you about the importanceof critical minerals in semiconductors.
Indeed, critical mineralsare very important for semiconductors.
For example, gallium, indiumthose are being used in the industry,
but those are also consideredcritical materials.
(11:26):
And the part of the research
we are doing, among many other researchersis to develop new semiconductors,
then potentially can usemore abundant elements.
And have more enhanced functionality.
How hard will it beto adopt other materials
that are more common or easier to useto replace the current critical minerals?
(11:48):
As you also mentioned earlier,for any new semiconductor material,
it often takestime for the industry to adopt.
There's always a questionabout compatibility
with semiconductor processing.
The existing ones, among other factors.
So it's not an easy
answer to your question, but,I can give one example.
(12:12):
For example, in the materialwe are working on,
we are adding new elementsinto gallium nitride.
So potentiallywe can have enhanced functionality
by using less gallium or less indium,and therefore have less demand
on the critical mineralswithout affecting the processing too much.
(12:33):
How has NSF support impacted your workso far?
I'm very gratefulfor the support from NSF.
NSF not only provides support
for graduate students,materials, supplies,
but it provides the immense flexibilityfor us to explore
the unknown domain in semiconductorand related research.
(12:58):
It also help us to build a networkto collaborate and connect
with other researchers,
not only at the University of Michigan,but also in other institutions.
So this is reallya very important resource
for usand for university research to continue
to make breakthrough advancesin many sectors.
(13:20):
For my last question today, I want to askyou about the future of semiconductors.
Where do you see it
developing or where do you see your workgoing in the next few years?
So it's a very exciting timefor semiconductor research,
not only because it is importantfor our existing microelectronics,
for example, to make our computers,cell phones to be more efficient, consume
(13:43):
less power, to make our communicationto be faster, to be more secure.
But also it's important to open upfuture opportunities,
for example, for medical, for healthcare,for future quantum technologies.
These are some of the most exciting timefor semiconductor
research from a historical point of view.
(14:05):
And for my own researchat the University of Michigan,
we have very talented colleaguesworking in materials,
in device systems,circuits and applications.
So I'm very fortunate to be a facultymember at the University of Michigan.
So basically, for my own research,I focus on the development
(14:26):
of next generationwide bandgap semiconductors.
And then semiconductorscan potentially be used
to help make more efficient electronic
optoelectronic devices,and also have some implication
to make future quantum technologiescloser to our life.
(14:47):
Special thanks to Zetian Mi.
For the Discovery Files, I'm Nate Pottker.
You can watch video versions
of these conversations on our YouTubechannel by searching @NSFscience.
Please subscribe wherever you get podcastsand if you like our program,
share it with a friendand consider leaving a review.
Discover how the U.S.
National Science Foundationis advancing research at NSF.gov.
This is the Discovery Files podcastfrom the U.S.
National Science Foundation.
Semiconductors are the backboneof most modern electronic devices,
from smartphones and home appliancesto MRI scanners and satellites.
Breakthroughs in semiconductorsand microelectronics
will be key to overcoming limitsin critical areas, including artificial
(00:23):
intelligence, quantum computing,manufacturing and communications.
We're joined by Zetian Mi,
professor of electrical engineeringand computer science
at the University of Michigan.
His group is working on a new classof semiconductors
with great potential for next generationmicroelectronic devices.
Professor Mi,thanks so much for joining me today.
Thank you very much Nate.
It is my great honor and pleasureto have this opportunity to talk to you.
(00:46):
So I need to ask you about wurtziteferroelectric nitrites.
What is this?
So my group is working on three nitridesemiconductors.
This is materialthat's commonly used in our daily lives.
For example,we use this material for LED lighting.
They are also in our cell phonesand literally everywhere.
(01:09):
And the second most producedsemiconductors on this planet
next only to silicon.
So this material has been around, but for decades.
This materialis known to be piezoelectric.
Let me briefly explain what piezoelectric is.
So this material has fixedthe polarization inside of the material.
(01:33):
And, when you apply electric field,you can generate a string and vice versa.
So they can also be used as sensors.
So the ferroelectric
is a subset of the piezoelectric family.
By saying ferroelectricwe mean the electrical polarization
in the materialcan be reversed back and forth.
(01:56):
When we apply an external electric field.
Ferroelectric is not new, first discovered
around 100 years ago, 1920by a graduate student
when he was doing PhDat University of Minnesota.
But for nearly 100 years, the ferroelectric materials
are mostly oxide based.
Oxide based feroelectricthey have been used almost everywhere.
(02:20):
For example, in sensors, in industrysettings, in medical devices,
in ultrasonic.
However, the oxide ferroelectricalso has some fundamental limitations.
For examble,they are not stable in harsh environments.
It’s very difficultto make them compatible with a mainstream
semiconductor processing, and thereforelimit some of their applications.
(02:45):
And here we have one of the most producedsemiconductor material.
And now we can turn it into ferroelectric.
You can imagine the enormous opportunitiesthis can open.
And that'swhat we are really excited about.
So how do you store informationinside an electric field?
So electric field in the semiconductor
(03:08):
can have positive or negative directions.
Which means we can switchthe direction back
and forth for ferroelectric material
and then give us the opportunityto store the information.
For examplewe can define a positive direction
polarization as the information one,a negative as zero right.
(03:31):
Then we can store the information.
We can electrically reversethe polarization,
which means we can writeor reset the information in the material.
Or we can read the materialby applying a electrical signal.
We can read the information stored inside.
The most beautiful part ofthis is the information is stored there
(03:54):
without applying any external bias.
So once you set the polarization, there,
it will stay therewithout supplying any external power.
So this is a so-called nonvolatilememory device.
And so imagine if we can build
atomic scale memory cellswith a very little power consumption,
(04:17):
and we can integrate billions or trillionsof them on a very small size chip.
And that's going to really revolutionize
computingcommunication in the years to come.
So what is the benefit of lowerpower consumption with semiconductors?
Computing communication is consumingenormous amount power as we speak.
(04:40):
And with the AIthis is going to grow exponentially.
So how to reduce the power consumptionat the device level will be very critical.
Now let's first talk about this,this device power consumption.
There are many factors that will affectthe device power consumption.
For example, for memory device. Right.
(05:00):
How much powerwe need to reset or right to the signal,
how much power we need to useto read the signal, or how much power
we need to use to store the informationto maintain the information.
So what's really great about thismaterial is nonvolatile.
We do not need to have extra powerto maintain the information.
(05:24):
Now come back to the power consumptiondue to the writing
or reading for a memory device or,other devices.
It directly related to the efficiencyand also relate to the device size.
And for the wurtziteferroelectric nitrides.
Nowadays we can grow them atomic layerby atomic layer
(05:45):
so we can make them very, very small.
And therefore the power consumptioncan be drastically reduced
together with very high integrationdensity billions,
billions of devices can be integratedon a very small size chip.
What is the unique polarization capabilityin this material?
Yes. I'm glad you asked.
So for the wurtzite ferroelectric?
(06:08):
There have been interest and studies bymany research groups but for a long time.
There is a fundamental questionis for this wurtzite ferroelectric.
Once we switch the polarizationthen we have all the this
polarization within the same material,just like a bar magnet right.
(06:29):
The north and south pole.
When you try to put them together withinone material, how can they be stabilized?
And specificallyin the wurtzite ferroelectric?
When we switch the polarization
only part of the material,the polarization is switched.
So there will be domainsof different polarization.
(06:52):
At the interface, we may have two positiveelectric field facing each other.
How can this be stabilized.
This has remained a fundamental question.
So that's one of the studiesthat we recently published.
We showed that.
And and this dummy interface,
we have a new atomic scene structure
(07:14):
and this atomic structure different
from the host materialand has unbonded electrons,
which can stabilize the polarizationdiscontinuity.
Not only that, this electron density
is much higher than thatin the traditional gallium
nitride transistors,that this is like 100 times higher.
(07:38):
So provides future opportunities to design
nanoscale device with better performance.
How is this discoverygoing to really impact
the next generation of semiconductorsthat people see in their devices.
It’s going to impactin several different ways.
Gallium nitride devices are alreadyin many business sectors, right?
(08:03):
Almost in our daily lives.
And now we have this ferroelectricity
and it can enhance the performance
functionality of existing devices.
For example, it can make our cell phoneto have stronger, signal
less noise to operate more efficiently,
and secondly, it also broadensthe scope of the traditional oxide
(08:29):
ferroelectric beyondwhat can possibly be done.
Oxideferroelectric is a wonderful material.
However, this material has some challengeswhen operating in harsh environment.
For example in aerospace,
or spacecraft, in electrical vehicleswhere you often
(08:49):
have very high temperatureor other extreme conditions.
These wurtzite ferroelectric nitrides
are known to be very stableat very high temperature.
Up to 1000 degree Celsius.
That can have immediatelyimportant applications.
And also this wurtziteferroelectric nitrides can be grown
(09:11):
or synthesizeatomic layer by atomic layer.
And you can really scale these to verysmall size and with excellent performance.
So that will helpto make electronic devices
with better performancewith high integration density.
And also these material can be integratedwith the mainstream
(09:33):
electronics silicon and gallium nitridewhich will all enhance
the functionality of our futuremicroelectronics.
The exact scope and impact remainsto be seen, but,
many colleagues in academia,in the industry, we are very excited
with the enormous potentialof this new class of semiconductors.
(09:56):
Are there challengesgetting buy in from industry partners
when you develop a new materialor a new strategy
to introduce these materials into devicesthat they are currently producing?
Yes. As you correctly mentioned,for any new material,
there are important considerationshow they are going to be adopted
(10:18):
by the industry, how this is going to beintegrated with their production lines.
Some materialsmay have wonderful properties,
but if they cannot be adopted by industry,
they will only remainas a subject of research interest.
Very fortunately,for this material family.
It is based on an existing material,gellium nitride
(10:41):
is the secondmost produced semiconductor in industry,
and we only add 1or 2 elements into this material.
And then we can transform this material
to how wonderful propertiesnot existing before.
As a matter of fact,this material has already been
adopted in our next generationcell phones.
(11:04):
And we'll see more of those in the future.
I want to ask you about the importanceof critical minerals in semiconductors.
Indeed, critical mineralsare very important for semiconductors.
For example, gallium, indiumthose are being used in the industry,
but those are also consideredcritical materials.
(11:26):
And the part of the research
we are doing, among many other researchersis to develop new semiconductors,
then potentially can usemore abundant elements.
And have more enhanced functionality.
How hard will it beto adopt other materials
that are more common or easier to useto replace the current critical minerals?
(11:48):
As you also mentioned earlier,for any new semiconductor material,
it often takestime for the industry to adopt.
There's always a questionabout compatibility
with semiconductor processing.
The existing ones, among other factors.
So it's not an easy
answer to your question, but,I can give one example.
(12:12):
For example, in the materialwe are working on,
we are adding new elementsinto gallium nitride.
So potentiallywe can have enhanced functionality
by using less gallium or less indium,and therefore have less demand
on the critical mineralswithout affecting the processing too much.
(12:33):
How has NSF support impacted your workso far?
I'm very gratefulfor the support from NSF.
NSF not only provides support
for graduate students,materials, supplies,
but it provides the immense flexibilityfor us to explore
the unknown domain in semiconductorand related research.
(12:58):
It also help us to build a networkto collaborate and connect
with other researchers,
not only at the University of Michigan,but also in other institutions.
So this is reallya very important resource
for usand for university research to continue
to make breakthrough advancesin many sectors.
(13:20):
For my last question today, I want to askyou about the future of semiconductors.
Where do you see it
developing or where do you see your workgoing in the next few years?
So it's a very exciting timefor semiconductor research,
not only because it is importantfor our existing microelectronics,
for example, to make our computers,cell phones to be more efficient, consume
(13:43):
less power, to make our communicationto be faster, to be more secure.
But also it's important to open upfuture opportunities,
for example, for medical, for healthcare,for future quantum technologies.
These are some of the most exciting timefor semiconductor
research from a historical point of view.
(14:05):
And for my own researchat the University of Michigan,
we have very talented colleaguesworking in materials,
in device systems,circuits and applications.
So I'm very fortunate to be a facultymember at the University of Michigan.
So basically, for my own research,I focus on the development
(14:26):
of next generationwide bandgap semiconductors.
And then semiconductorscan potentially be used
to help make more efficient electronic
optoelectronic devices,and also have some implication
to make future quantum technologiescloser to our life.
(14:47):
Special thanks to Zetian Mi.
For the Discovery Files, I'm Nate Pottker.
You can watch video versions
of these conversations on our YouTubechannel by searching @NSFscience.
Please subscribe wherever you get podcastsand if you like our program,
share it with a friendand consider leaving a review.
Discover how the U.S.
National Science Foundationis advancing research at NSF.gov.
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