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Advanced RF Calibration Techniq

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 Advanced RF Calibration Techniq Powered By Docstoc
					                                             Advanced RF Calibration
Innovating Test
Technologies                                       Techniques
for better
measurements
faster




                  presented by
                  Anthony Lord
                  Cascade Microtech Europe
                  www.cascademicrotech.com
                  anthony.lord@cmicro.com
                   RF & Microwave Measurement Techniques, Methods and Troubleshooting



 Innovating Test
                   Where is the reference plane?
 Technologies
 for better
 measurements
 faster




                   • In order to know exactly what we are measuring all errors up to
                     the probe tip must be removed
                       – This includes internal VNA errors after the sampler, the cables and
                         probes
                   • Normally a coaxial calibration will remove all errors to the end of
Links                the coax cable - For on-wafer measurements we also need to
App Notes –          correct for the losses in the probes
On-wafer VNA
                       – Thus calibration standards are required to be available at the probe
                         tip
                   RF & Microwave Measurement Techniques, Methods and Troubleshooting


                   What is the basics of the Vector
                   Network Analyser?
 Innovating Test
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 for better
 measurements
 faster




                                            a0   b0
                                                          a0                        a1
                                                                        X
                                                               b0      Error             b1
                                                                      Adapter
                                            Perfect
                                                                                          DUT
                                          Reflectometer
                                Perfect                                 Y
                                Switch                    a3           Error        a2
                                                                      Adapter
                                                               b3                        b2
                                            a3   b3                 8 Error Terms
Links
App Notes –
On-wafer VNA
                   RF & Microwave Measurement Techniques, Methods and Troubleshooting


                   What are the calibration options and
                   standards?
 Innovating Test
 Technologies
 for better
 measurements      • Un-corrected measurements
 faster
                       – Poor accuracy, but fast?
                       – Rarely used
                       – Easy (no calibration required)
                    • Response calibration
                        – Low accuracy
                        – Used only when speed is more
                          important than accuracy
                        – Only require one standard
                    • Full 2-port calibration
                        – Highest accuracy
                        – Removes following errors
Links                       –   Directivity
App Notes –                 –   Source/load match
On-wafer VNA                –   Reflection/transmission tracking
                            –   Cross-talk
                        – Requires up to 7 standards
                   RF & Microwave Measurement Techniques, Methods and Troubleshooting


                   Which Full 2-port calibration
                   techniques can I use?
 Innovating Test
 Technologies
 for better
 measurements
 faster




                        •   Thru-Reflect-Match (LRM)
                        •   Thru-Reflect-Reflect-Match (LRRM)
                        •   Thru-Reflect-Line (TRL or LRL)
                        •   Short-Open-Load-Thru (SOLT)
                        •   Short-Open-Load-Reciprocal (SOLR)
Links
App Notes –
On-wafer VNA
SOLR
LRRM Verify
VNA Guide
                   RF & Microwave Measurement Techniques, Methods and Troubleshooting



 Innovating Test
                   Why should I use SOLT calibration?
 Technologies
 for better
 measurements
 faster
                                       • Short-Open-Load-Thru Calibration
                     Short                - Most Commonly Used Cal
                                            - all standards must be perfectly known (cal
                                              kit)
                     Open                   - open has capacitance (often negative)
                     (probes in air)
                                            - short and load have inductance
                                            - not inherently self-consistent
                     Load                   - uses off-wafer standards
Links
                                            - available on virtually every vector network
App Notes –
                                              analyser
On-wafer VNA          Thru                  - performs reasonably well if accurate models
VNA Guide                                     of calibration standards can be determined
                                            - sensitive to probe placement
                   RF & Microwave Measurement Techniques, Methods and Troubleshooting



 Innovating Test
                   Why should I use SOLR calibration?
 Technologies
 for better
 measurements
 faster
                            • Short-Open-Load-Reciprocal Calibration
                        Short  – Like SOLT but with general Thru standard
                                            – reciprocal thru S12 = S21
                                            – tolerant to high loss or highly reactive insertion
                       Open                     standard
                       (probes in air)
                                         – convenient for use with probe cards
                                            – fixed probe spacing would otherwise require
                       Load                     custom standards
                                         – not available on vector network analysers
Links
App Notes –
                                            – requires Cascade Microtech software
On-wafer VNA
                      R-Thru                    (WinCal)
SOLR                                     – still needs accurate models of calibration
                                           standards
                   RF & Microwave Measurement Techniques, Methods and Troubleshooting



 Innovating Test
                   Why use an orthogonal calibration?
 Technologies
 for better
 measurements
                             |S21|
 faster
                               1.0



                               0.5
                                                                 Orthogonal SOLT
                                                                  Orthogonal LRRM
                               0.0

                                         Orthogonal SOLR
                              -0.5
                                                                 Straight LRRM


                              -1.0
                                     0      5    10    15   20   25    30    35     40   45   50
                                                                 [GHz]
Links
App Notes –
On-wafer VNA
                     • Insertion loss measurements made of an orthogonal
SOLR                   CPW thru’ line using straight LRRM and orthogonal
                       LRRM, SOLT and SOLR calibrations
                   RF & Microwave Measurement Techniques, Methods and Troubleshooting



 Innovating Test
 Technologies
                   Why should I use LRRM calibration?
 for better
 measurements
                               • Cascade Microtech Calibration Research
 faster
                                  – Line-Reflect-Reflect-Match Calibration
                      Line             – available in WinCal
                                       – only requires match standard on one port
                                       – like TRL only Match acts as infinitely high loss
                                         line
                     Reflect
                                       – broadband calibration
                                       – one transmission line standard allows fixed probe
                                         spacing calibration
                     Reflect           – Thru (line) delay, Match resistance must be
Links                (probes in air)
                                         known
App Notes –
On-wafer VNA
                                       – measurements referenced to laser trimmed
                     Match               resistor
LRRM Verify
VNA Guide                              – uses off-wafer standards
                                           – Impedance Standard Substrate
                                       – same standards as SOLT only no need for cal kit
                   RF & Microwave Measurement Techniques, Methods and Troubleshooting



 Innovating Test
 Technologies
                   Why should I use TRL calibration?
 for better
 measurements
 faster
                             • Research by the U.S. National Institute of
                               Standards and Technology
                    Thru
                                – Multi-line TRL (Thru-Reflect-Line)
                                    – optimal weighted average of standard
                                      measurements
                                 – uses multiple transmission lines as standards
                   Reflect          – measurements referenced to line impedance
                                    – limited frequency range (e.g. 3 lines for 2-18
Links
                                      GHz)
App Notes –                      – requires multiple probe spacing
On-wafer VNA           Line(s)      – not suitable for fixed spacing probes
LRRM Verify
VNA Guide
                                    – standards need to be on-wafer (with DUT)
                                    – fully automatic cal achievable with motorized
                                      positioners
                   RF & Microwave Measurement Techniques, Methods and Troubleshooting


                   Which calibration is best for my
                   application?
 Innovating Test
 Technologies
 for better
 measurements
 faster
                                 Z0                Inherently   Probe Card   Absolute
                              Reference            Consistent   Support      Accuracy

                   SOLT       Trimmed Resistor        No          Fair         Fair

                   NIST TRL   Transmission Lines      Yes         Poor        Best

                   TRL        Transmission Lines      Yes         Poor        Poor-Fair

                   LRRM       Trimmed Resistor        Yes         Fair        Very Good
Links
App Notes –        LRM        Trimmed Resistor        Yes         Fair        Fair
On-wafer VNA
                   SOLR       Trimmed Resistor        Yes         Best        Good
SOLR
LRRM Verify
VNA Guide
                   RF & Microwave Measurement Techniques, Methods and Troubleshooting


                   What is the most accurate calibration
                   technique?
 Innovating Test
 Technologies
 for better
 measurements
 faster
                   • NIST Calibration and
                     Verification Software
                   • Verification standards
                     are GaAs CPW lines
                   • 45MHz to 40GHz
Links
                   • LRRM compares with
App Notes –          system drift limit
On-wafer VNA
110GHz Comp
                   • SOLT /LRM
SOLR                    – growing error w/freq
LRRM Verify
                        – possible cal kit error
VNA Guide
                        – possible ref plane
                          error
                   RF & Microwave Measurement Techniques, Methods and Troubleshooting


                   How does a manual calibration
                   compare to an automatic calibration?
 Innovating Test
 Technologies
 for better
 measurements
 faster
                                    Worst Case Accuracy to 40GHz
                        Four Manual Calibrations           Ten Semi-Auto Calibrations



                      15% Error -                        5% Error - 0.3% spread
                      10% spread




Links
App Notes –
On-wafer VNA
LRRM Verify
VNA Guide

                     Semi-auto Prober is faster and far more repeatable!
                   RF & Microwave Measurement Techniques, Methods and Troubleshooting


                   How repeatable are the calibration
                   standards?
 Innovating Test
 Technologies
 for better
 measurements
 faster
                     Worst case deviation


                                            10 LRRM calibration
                                            verifications using NIST Verify
                                            software                          • Impedance
                                                                                Standard
                                                                                Substrate
                                                                                Standards
Links
App Notes –
                                                                                are very
On-wafer VNA                                                                    repeatable
110GHz Comp
LRRM Verify
VNA Guide
                                              Frequency (GHz)
                   RF & Microwave Measurement Techniques, Methods and Troubleshooting


                   What are the Problems with Over
 Innovating Test
 Technologies      Temperature Microwave Measurements?
 for better
 measurements
 faster
                     • Frost build-up at low temperatures
                         – A small enclosed measurement environment purged to
                           < - 55 degC
                     • System drift of probes and cables over
                       temperature
                         – Calibrate with probes and cables soaked at temperature
                     • Unknown load standard on ISS
                         – A thermally isolated auxiliary chuck is required to mount
Links                      the ISS
App Notes –
                     • Wafer expansion/contraction
HF Over temp
HF Over temp2
                         – Probe station compensation capability for die to die
Thermal Meas
                           stepping
                   RF & Microwave Measurement Techniques, Methods and Troubleshooting



 Innovating Test
                   What Can I do to avoid these problems
 Technologies
 for better
 measurements                                                    •   Dry, Frost Free
 faster
                                                                     environment
                                                                 •   Auxiliary Chucks
                                                                 •   Top-Hat


Links
App Notes –
HF Over temp
HF Over temp2
Thermal Meas
Data sheets –
S300
Summit RF
Summit 9101
RF-1
                   RF & Microwave Measurement Techniques, Methods and Troubleshooting



 Innovating Test
                   Over Temperature Probing Techniques
 Technologies
 for better
 measurements
 faster
                   • Calibrate with probes, DUT and ISS at ambient
                       – Good initial calibration accuracy
                       – Phase error at temperature due to probe and cables
                         expansion (not recommended)
                   • Calibrate with probes, DUT and ISS at temperature
                       – Poor calibration due to unknown load standard
                       – Little system drift (not recommended)
Links              • Calibrate with probes and DUT at temperature, and
App Notes –          ISS at ambient (Recommended)
HF Over temp
HF Over temp2
                       – Good initial calibration accuracy
Thermal Meas           – Little phase error due to probes and cable expansion
                   RF & Microwave Measurement Techniques, Methods and Troubleshooting


                   Calibration Stability at 200°C for a 25°C
 Innovating Test
 Technologies
 for better
                   Calibration
 measurements
 faster




Links
App Notes –
HF Over temp
                      Calibration stability unacceptable
HF Over temp2
                           • Probe still changing after 15 mins
Thermal Meas
                           • Calibration stability exhibits greater degradation with
                           increasing frequency
                   RF & Microwave Measurement Techniques, Methods and Troubleshooting



 Innovating Test
                   Auxiliary Chuck Temperature
 Technologies
 for better
 measurements                            30                                                                               220
 faster                                                                                                                   200
                                         20
                                                                                                                          180




                                                                                                    Temperature (deg C)
                                         10
                   Temperature (deg C)




                                                                                                                          160                           ISS Stage Temperature
                                          0                                                                               140
                                         -10 0   2   4   6   8     10    12   14     16   18   20                         120                           Chuck Temperature
                                         -20                                                                              100
                                                                 ISS Stage Temperature                                     80
                                         -30
                                                                 Chuck Temperature                                         60
                                         -40
                                                                                                                           40
                                         -50                                                                               20
                                         -60                                                                                0
                                         -70                                                                                    0   5   10   15    20     25    30    35    40   45
                                                             Time (Mins)                                                                          Time (Mins)




Links
                                         ISS Temperature stays between -10°C and 60°C over the
App Notes –
                                         whole thermal chuck range - Reducing error from 50 ohm
HF Over temp
HF Over temp2
                                         load standard
Thermal Meas
                   RF & Microwave Measurement Techniques, Methods and Troubleshooting



 Innovating Test
                   Think About Testability Before Design
 Technologies
 for better
 measurements
 faster              • RF Performance
                        – Pad configuration (GS Vs GSG)
                        – Probe pitch
Links                • Ability to Physically Probe
App Notes –
Layout Rules
                        – Pad size
WPH900 Rules            – Pad height
On-wafer VNA
Data sheets –
                        – Distance between probes
Probe Stations          – Number of contacts per side
ACP Probes
                     • Calibration
Eye-Pass Probe
HPC Probe               – Paths
Probe Guide
                        – Best calibration methods
                   RF & Microwave Measurement Techniques, Methods and Troubleshooting



 Innovating Test
                   What pad sizes should I use?
 Technologies
 for better
 measurements
                   • Recommended minimum pad
 faster
                     is 80um x 80um for ACP
                     Probes when performing
                     automated measurements
Links
                   • Smaller pad dimensions can be
App Notes –
Layout Rules         used for manual probing
WPH900 Rules
                   • HPC Probe Allows 40um x
On-wafer VNA
Data sheets –
                     70um manual probing
Probe Stations
ACP Probes
                   • Passivation height must be
Eye-Pass Probe       considered
HPC Probe
Probe Guide
                   • Pad height variation must not
                     exceed 25um
                   RF & Microwave Measurement Techniques, Methods and Troubleshooting



 Innovating Test
                   What about probe positioning?
 Technologies
 for better
 measurements
 faster




                                               200um




                                                           >500um
Links
App Notes –        • RF probes should have more than 200um separation
Layout Rules
                     to avoid cross-talk
On-wafer VNA
Data sheets –      • All pads must be on top surface
ACP Probes
Probe Guide
                   • All grounds should be connected together
                   • Adjacent devices should be >500um away for mm-
                     wave measurements
                   RF & Microwave Measurement Techniques, Methods and Troubleshooting



 Innovating Test
                   What do I need to consider regarding
 Technologies
 for better
                   calibration?
 measurements
 faster
                   • For corrected two-port S-parameter
                     or response calibration a thru’
                     standard is always required.
                      – If individually mounted RF probes
                        are used, they should preferably
                        be adjacent
Links
App Notes –
                      – If the RF ports are orthogonal or
Layout Rules            ‘horse shoe’ SOLR calibration
On-wafer VNA
                        method must be used
SOLR
Data sheets –         – If a fixed RF probe card is used
ISS Family
                        SOLR and a custom ISS is
                        preferred
                   RF & Microwave Measurement Techniques, Methods and Troubleshooting


                   What are the problems with probing
                   Silicon wafers with Aluminium pads?
 Innovating Test
 Technologies
 for better
 measurements
 faster
                   • Aluminium Oxide on Aluminium pads
                       – A layer of Al Oxide will grow on the pad surface when left
                         in air
                          – This leads to possible contact resistances and variable
                             contact resistance with time
Links
App Notes –
                   • Conductive substrate increases parasitic reactance
W vs BeCu              – Pad and interconnect capacitance and inductances
On-wafer VNA             become more significant during device measurement
Quick Guide –
                          – De-embedding of pads and interconnects is required
Tungsten Probe
Data sheets –      • Limitations of Pad Parasitic Removal methods
ACP Probes
                       – The larger the pads and smaller the device, makes de-
Probe Guide
                         embedding more difficult to achieve
                   RF & Microwave Measurement Techniques, Methods and Troubleshooting


                   How do I overcome the contact
                   resistance problem?
 Innovating Test
 Technologies
 for better
 measurements
 faster
                   • Must penetrate Oxide on Aluminium pads
                     – Standard BeCu tips are usable
                          – but multiple touchdown are required to remove the oxide
                            layer from the pad
                       – Tungsten tips are superior
Links
                          – but the tungsten tip will also oxidise in air
App Notes –
W vs BeCu
                          – Probing Al pads works well with W probes since both
On-wafer VNA
                            metals are very hard and rugged and perform a self-
Quick Guide –
                            cleaning action when contact is made
Tungsten Probe               – Lower contact resistance
Data sheets –                – Better stability over time and temperature
ACP Probes
                             – Improved measurement repeatability
Probe Guide
                   RF & Microwave Measurement Techniques, Methods and Troubleshooting


                   What is De-embedding?
 Innovating Test
 Technologies
 for better                                     Eliminate
 measurements                                   parasitic
 faster            Reference                    effects
                                                                              Reference
                                                                               plane
                    plane
                                               through
                                             De-embedding

                                                                                  - After calibration,
                                                                                  the measurement
                                           Source + Substrate
                                                                                  reference plane is at
                                                                    Ground
                          Ground
                          Ground                                    Ground        the probe tip
                                                                                  - What is measured
                                                            Drain    Signal
                           Signal
                          Signal    Gate                            Signal        is the response of
Links                                                                             the device and the
App Notes –
                          Ground                                    Ground
                                                                    Ground
                                                                                  parasitics associated
On-wafer VNA              Ground       Source + Substrate                         with the pads
Data sheets –
WinCal
                   RF & Microwave Measurement Techniques, Methods and Troubleshooting


                   De-embedding and Verification
                   Test Structures
 Innovating Test
 Technologies
 for better
 measurements
 faster
                    OPEN                               SHORT




                    DUT                                 THRU
Links
App Notes –
On-wafer VNA
Data sheets –
WinCal
                   RF & Microwave Measurement Techniques, Methods and Troubleshooting


                   De-embedding from OPEN and
                   SHORT
 Innovating Test
 Technologies
 for better
 measurements
 faster




                   The parasitics of the OPEN consist only of parallel elements to
                   the DUT
                       More importance for high impedance devices
Links
App Notes –
                   The parasitics of the SHORT consist only of series elements to
On-wafer VNA       the DUT
Data sheets –
                       More importance for high impedance devices
WinCal
                   Use of Z and Y correction also helps eliminate residual cal errors
                   RF & Microwave Measurement Techniques, Methods and Troubleshooting



 Innovating Test
                   PPR Corrected H21 Measurement
 Technologies
 for better
 measurements
                   0.25 µm CMOS Transistor
 faster


                                                              H21
                            60



                            40
                                                     Corrected for pad parasitics
                                                           FT = 33 GHz
                                       As measured
                            20
                                       FT = 25 GHz


Links                        0
App Notes –
On-wafer VNA
Data sheets –               -20
WinCal                            .1                 1                  10          100
                                                         FREQUENCY (GHz)
                  RF & Microwave Measurement Techniques, Methods and Troubleshooting


                  Discussion, links and further
                  information
Innovating Test
Technologies
for better
measurements
faster
                  • Any questions?

                  • Please note that the CD handout has many
                    application notes, data sheets and information on all
                    areas covered today

                  • Contact Cascade Microtech for further discussion




                           www.cascademicrotech.com

				
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