(upbeat music)
- Hello everyone, welcome to Tektronix Innovation Forum.
And in this session,
we will talk about Wide Bandgap Applications
and Validation Test Challenges.
My name is Yogesh Pai
and I'm Product Manager for Power Solutions at Tektronix.
And in this session I'm being joined by Srikrishna,
who is our senior technologist for power solutions.
Let's get started.
Here is the agenda for today's presentation.
We will start with the understanding
of Wide Bandgap technology, a typical test workflow.
Talk about some of the test challenges
and potential solution
to address some of those test challenges.
Let's start with the basic question.
What is Wide Bandgap?
and why are we talking about it these days?
All traditional power electronic designs
have historically been based on Silicon technology.
Compared to these traditional Silicon power devices,
Wide Bandgap power semiconductors, like Silicon carbide
and gallium nitride have special characteristics.
These characteristics translate into clarity
when we investigate the device specifications.
Given the same dye size and thickness,
the Wide Bandgap devices can provide
higher breakdown voltage, higher current,
higher operating temperature
and most importantly offer faster speeds
and lower switching losses compared to Silicon devices.
All of these characteristics,
translates into higher energy efficiency
at a reduced form factor
making it an ideal choice for the designers.
As the adoption of Wide Bandgap devices is increasing,
the cost of manufacturing and integrating them
into traditional Silicon designs is reducing day by day,
making it a win-win situation, both for the designers
and the consumers.
Because of these advantages, the Wide Bandgap devices
have been named as a key enabler
to revolutionize power conversion in the recent years.
And they are available in the market
both as discrete devices and power modules.
Silicon Carbide and Gallium Nitride
are two of the most popular Wide Bandgap technology devices
available in the market today.
There are several design considerations
that are required before adopting
the Wide Bandgap technology in the Silicon designs.
Some of these key design considerations include;
choosing a robust reverse recovery diode in the designs,
choosing components such that we have near lossless
switching parameters,
operating at the highest switching frequencies
and high temperatures,
exploring newer topologies
to help achieve higher performance in various SMPS designs
and optimize designs that can help go to market faster.
Choosing correct Wide Bandgap devices like SiC MOSFETs
or GaN FETs
for different applications
depends on the operating voltage levels
and switching speeds.
SiC devices are most suited for medium to high voltages
typically or and about 1.2 kV range.
This includes application like
transportation, wind energy and power grids.
GaN devices are most suited for lower voltages
typically in the range of 600V or less.
This includes application like
consumer electronics, power supplies, chargers and UPS.
And in the range between 600 V and 1.2 kV,
that is where both SiC and GaN have equal play
based on the application needs.
This area includes applications like
solar inverters and EV/HEV inverters and motor drives.
The adoption of Wide Bandgap in the green power segment
promises sustainability
and diversifying the energy supplies.
While its adoption in the automotive segment promises
to reduce carbon footprint and conserve fossil fuel.
So what are some of the high level test challenges?
Devices based on Silicon Carbide and Gallium Nitride
can switch at much higher frequencies
and also have far lower leakage compared to Silicon.
This also means that there is a need
for sourcing higher voltages in testing
and there is also a need
for greater current measurement sensitivity.
It can be quite challenging to characterize
these new devices at very low levels of current.
The instrumentation used must be capable
of characterizing significantly higher rated voltages
and peak currents than even before
while providing the measurement resolution
and accuracy characterizing these new material devices.
Here, we have a typical power converter workflow.
For example, this could be an EV inverter workflow.
The workflow starts
with component characterization on the left,
then goes into the simulation block in the center,
and finally ends with the validation block on the right.
The characterization block is particularly focused
on testing Wide Bandgap components,
such as MOSFETs IGBTs,
both in its discrete and module forms.
An engineer working in this block
is interested to define the test limits,
characterize the components
across various operating frequencies and temperature range.
This is also sometimes referred to as
static characterization.
This helps the engineer to publish the device models
and component data sheet
which can then be referred
to build application reference designs
and later an entire inverter system.
Next, we have the simulation block.
Here, the engineers integrate the components
into the designs and create a spice model.
As the designs solidify, the engineer's work
on creating and simulating an entire inverter performance.
As you know, the cost of producing an actual hardware
and testing is quite high.
So ensuring we have captured the right test data
and covered all the test cases to evaluate the performance
at simulation stage, becomes critical.
Finally, we have the validation block.
Here, the engineers are working
on some early reference designs and end systems.
This is where components that were characterized
at the first stage, get integrated.
Some of the common focus areas include:
gate driver reference designs,
designing for highest efficiency, debugging failure
and publishing the reference design documentation.
And for system engineers,
it's more around trying to reduce the board size,
gaining access to the test signals
and meeting the OEMs requirements.
Let us now talk about typical test challenges
in the characterization and the validation blocks.
First, we shall talk briefly around the test challenges
during the characterization stage.
Although this presentation will focus mainly
on the validation testing areas in detail.
When testing at high voltage levels,
safety is of utmost concern.
Some SMUs can source voltage up to three kilovolts.
So precautions must be taken
to ensure that the operator is not exposed
to unsafe voltages.
Tektronix offers special cables
which are fully rated for use at three kilovolts
that the test system designer can use to interface
to the device under test.
The newer SMUs,
provide a rare panel safety interlock connection
so that the high voltage output is reduced to a safe level
if the interlock is not engaged.
Finally, if you are working around high voltages,
make sure that you're using proper safety gloves
so that you don't come in direct contact
with energized components or circuits.
When it comes to selecting instruments for high power,
it's recommended to use instruments
like Source Measure Units, SMUs.
These instruments provide,
integrated measurements, precise control
and a simple four quadrant operation
that SMU can source or sync precise voltage
and current signals.
When designing the GaN or SiC FET devices,
the main characteristic is to measure the family of curves.
This measurement can easily be performed
using the Source Measured Units
and a software that can control the SMUs
and graph the curves.
On the screen, you will see one such image of the curves
performed using the Keithley Dual-channel SMUs
and the KickStart Software.
An instruments such as a parametric analyzer
is also used quickly to get parametric insights,
perform fast and clear accurate Ivy characterization
across different operating frequency range.
Tektronix had recently hosted an informative webinar
that highlights key test challenges
around the second GaN component testing
with an emphasis on the five key measurements
that are shown here.
This webinar is available on demand
and we have added a link to that webinar on the slide
which will be available as part of the handouts
and you can check out that webinar offline.
With that, I would like to hand over
the rest of the presentation to Krishna,
to talk about characterization testing, validation testing,
test challenges and some potential solutions.
All to you Krishna.
- Thanks Yogesh.
We'll see about our second GaN components characterization.
As you know, a MOSFET is a voltage control device
which means it operates at the switch based
on a threshold voltage
applied to its gate terminal.
Some of the important parameters for MOSFET characterization
are measuring the gate voltage and drain current.
Observe the right-hand on the screen
which talks about the wafer
and also the key parameters to measure.
Our first key parameter is RdsON
which is on-state resistance.
It should be as low as it could be
to minimize the conduction losses.
As RdsON is small, it requires high current capability
to measure this parameter.
The second key parameter is gate charge.
This must be as low as possible
to minimize switching losses.
It's the critical parameter for switching performance
and gate drive circuit design.
It's also important to estimate
the switching loss parameter.
The five key test,
which are important for characterization
are (indistinct) drinkers, on-resistance that's RdsON,
leakage current, breakdown voltage and gate charge.
We are not going to discuss these things in detail.
Please refer to what Yogesh
had shared in the previous slide, the webinar link,
for more details.
Next, we will talk about the system validation
and the test challenges associated with it.
In the characterization stage,
most of discrete components get characterized
as per the data sheet values.
The challenge comes
when these components gets into circuit
and ready for use in a particular application.
The application board design needs to be tested
for different blocks within a circuit operation.
It is very critical that both parameters
are within the characterized values.
Some of the biggest challenges
working with SiC and GaN devices are,
the gate drive requirements.
Sic requires much higher voltage, a higher gate voltage
with a negative bias for turn-OFF.
On the other hand,
GaN require some much lower threshold voltage
requiring tight gate drive designs.
Wide Bandgap devices by the nature of their physics
also have a higher body diode voltage drop
that requires much tighter control of the time
and turn-ON, turn-OFF transitions.
Devices based on Wide Bandgap materials
are able to switch at much higher frequencies
than conventional silicone versions.
They also tend to have much lower leakage currents.
As a result, to properly characterize
the Wide Bandgap semiconductors,
testing required at higher voltages
and more sensitive measurement of currents.
Solving these challenges may be tough
for the power designers.
It's critical that
you have accurate electrical source and measure testing
when characterizing these high voltage devices
so that the right decisions can be made in a timely fashion.
Generally discrete components are tested
within a temperature chamber
and range of voltage and currents.
So safety becomes very important
to test worst case voltage and current,
and it is very important
during applying of high input voltages.
Many times probing access is a challenge
especially putting loops for the current probe access
It is recommended to use shunt resistor approach
to reduce the parasitics because of the loops.
The other challenges are floating challenges.
Devices are not grounded
and grounding through the scope would cause failures.
Common mode interference on switching
completely distorts the measurement.
What designers want to see are,
a control signals on switchboard power supplies
and current measurements across shunt resistors.
So IsoVu probe enables differential measurements
on floating side a bit faster signals
as low as one nanosecond.
IsoVu probe has fantastic accessories
to solve the probing and connectivity challenges.
Now let's look at the typical test system
for doing the measurements.
Typical equipment set up for WBG measurements.
You can see a illustration on the right side.
It needs AFG 31,000,
that's the external signal generator
to generate the stimulus.
This connects to the Isolated Gate Driver
and uses the double pulse test application
on the AFG to quickly generate the pulsers
with varying pulse rates.
Isolated Gate Driver is what turns the MOSFET on.
Another important piece of the test setup is oscilloscope.
This is very essential for debug and analysis.
The setup uses Tektronix 506-series MS probe.
This is used to capture and measure various
drain to source voltage, gate to source voltage
and drain currents.
Typical characteristic of an oscilloscope
that are essential are:
it is very important to have high ATC resolution.
12-bit ATC support can go higher but usually it fall
but it can go higher with hydrus acquisition mode.
This is very important because small details
and large signals requires high resolution
MSO5/6 series is a best in class noise sensitivity.
The 12-bit analog to digital converter
deliver 16 times the resolution of convention eight-bit ADC.
So in summary hydrus mode
delivers up to 16-bits of vertical resolution
for a final view of low frequency signals.
Another capable tool is
off-scope analysis we offer PC-based TekScope software
which lets you to analyze outside the scope.
This will let you use a scope hardware
for particular analysis
and do the post analysis on the software.
It is very important to optimize signal to noise ratio
in all measurement systems,
especially in digital devices
such as modern oscilloscope,
good measurement technique
requires keeping signals as large as possible
without clipping to minimize the effects of noise
and to maximize vertical resolution
then come into the probes.
That's a essential piece of the connectivity
The IsoVu probe.
Typically has a very high common mode rejection threshold
This probe is recommended to be used
to measure gate to source voltage,
specifically for Wide Bandgap semiconductors
since it also offers high bandwidth,
high common mode voltage,
we will see some more details in the next upcoming slide.
And finally, we also need a DC power supply
or a source measuring unit instrument
to supply the low voltage.
And we also need a good set up
automated software measurements
to do large set of analysis with minimal error
and lesser time.
We will see more details about this in the upcoming slides.
Let's look at some more details about the IsoVu probes.
IsoVu technology is the only differential probing system
for Wide Bandgap testing
solve the important attributes of this probe
which makes it suitable
for Wide Bandgap measurements are,
having high CMRR, high bandwidth up to one gigahertz
with less than 350ps Rise Time,
supporting up to 60 kV Common Mode
and having a wide input range upto 2500V via IsoVu probe.
Please note some of the probing challenges
for Wide Bandgap measurements
is interactions between the high and low side
of the power devices.
Violation of any specifications or designs
can lead to simultaneous conduction
and it blows up the device,
it degrates a device, increases searching loss
and also the efficiency of the system.
Question to ask is,
does your wide Bandgap measurements match
your expected results?
IsoVu gives you an accurate repeatable measurement
providing meaningful correlation with expected performance
IsoVu rejects common mode interference.
So you can see the true differential signal
CMRR is a critical, but often overlooked specification.
For example, can a firewall differential signal be measured
in the parameter of 100V common word signal?
Yes, with IsoVu probes it is.
Then we want to characterize entire Wide Bandgaps
(indistinct)
at the characterizing key parameters
such as gate voltage, data source voltage
and rain and source currents
characterize a time alignment of high and low side events,
optimize and fine tune switching characters traits
such as age rates or shoot ringing and dead time.
So in summary combination of IsoVu probe
with Tektronix 506-series MS probe
ensure the effective technique to debug
and fine tune WBG designs.
Let's look at key measurements
for system validation
WPT electrical measurements are done
by JEDEC and IEC standards.
JEDEC committee, JC 70 Wide Bandgap
power electronic conversion was formed in 2017.
It has two subcommittees DAC 70.1 and DAC 70.2
catering to GaN and SiC power devices.
We are part of JEDEC work group
and Tektronix is an active participant
and contributed to this group.
Next let's look at solve the scope base of power solution,
what we offer.
It talks about different measurements,
catering to the different states of the power devices
starting from input analysis,
then switching analysis parameters
magnetics for the transformers and the inductors
and output analysis,
which covers efficiency and repel measurements.
These tests helps to measure different parameters
in a single box solution.
Some of the other important measurements
on the input side are harmonic measurement
which supports various P compliance standards,
such as IEC 61,300-2, mil standard, EM40
and custom limits.
five dash power is a solution on scope,
which providing various switching loss parameters
which is very important for WBG measurements
such as energy on, energy off losses,
conduction loss, (indistinct) loss
internalized trends at RdsON,
rate of change of voltage and current
safe operating area for different flavors
like forward and reverse biases
and efficiency measurement.
Another important tool
which scope provides a spectrum view
to measure EMI parameters.
This is a standard option on most of the scopes
debugging embedded systems
often involves looking for some clues
that are hard to discover just by looking at one domain,
that is time domain.
The ability to look
at time and frequency domain simultaneously
can offer important insights.
Spectrum View enable simultaneous analog and spectrum views
with independent controls in each domain.
Next, the another important set of measurement
is Double Pulse Test.
It's also called a Dual Pulse Test.
Double Pulse Test is a method
to measure switching parameters
and evaluate a dynamic behavior of power devices.
Users of this application typically want to measure
the following switching parameters.
That's energy on energy off,
reverse recovery parameters
with turn-ON and turn-OFF regions.
These are very important test
typically as part of dynamic testing
and needs an external stimulus
using external generator like EFT 31,000
and usually switching parameters are analyzed
on the first and second pulse.
Diode Reverse Recovery is another class of measurements.
That is reverse recovery loss
of the body diode in the MOSFET to consider.
reverse recovery time of the diode
is a measure of the switching speed in the diode.
And this affects the switching losses
in the converter design.
So it's important to measure this reverse recovery.
Some of the reverse recovery parameters are,
TRR, IRR and QRR,
and also rate of change of voltage and current.
So this test is performed
to guarantee specifications of power devices
like MOSFETs and IGBTs.
If you look at the different stages of the measurement
it's a cycle of testing going through
a position of the wave forms,
using the test set of what we had discussed
in the previous slides.
Analyze through various complex algorithms and measurements
and finally make a report
out of this different measurements.
As you have seen
there are lots of measurements for system validation.
Post analysis on the acquired reforms
is important piece to arrive at the key decisions.
on the designs.
From the analysis perspective, building parametric results,
with multiple runs and multiple plots
it's very important to get the statistical results
which can usually can take days
to get it to conclude the results
and arrive at the decisions.
A dedicated Scope-based validation tool will help a lot
to do this analysis with much lesser report
by utilizing this automated test system
designer can improve
or test times reduce human computation errors,
improve repeatability of results
and traceability to which way
foam contribute to the failure.
And finally designers can share a specific session files
to different teams in the organization
to further analyze
and post persons with much more details
This becomes a powerful tool for the debug analysis.
Thank you and handing over to Yogesh
for further on the summary thoughts.
- Thanks, Krishna.
Okay, so we have seen that Wide Bandgap technology
is clearly the technology of the future.
The adoption of this technology requires designers
to overcome several significant challenges
in testing their power, semiconductor devices
highly sensitive testing equipment
improved test circuit design
and other considerations will be necessary
to properly characterize and validate these devices
Tektronix can help you
solve these problems related to Wide Bandgap.
As Wide Bandgap is one of the focus area
for Tektronix
when it comes to testing the power space.
So with limited time,
we could only cover brief details
in this presentation today.
However, if you need any further information
around Wide Bandgap testing
and how Tektronix can help solve your problems,
please contact your local Tektronix representative
or reach us on tek.com.
Thanks for attending this session today.