IHP Im Technologiepark Frankfurt (Oder) Germany IHP Im Technologiepark Frankfurt (Oder) Germany © All rights reserved 1/f Noise Measurements Falk Korndörfer

IHP Im Technologiepark Frankfurt (Oder) Germany © All rights reserved Outline Measurement system Noise current measurement with Stanford SR570 Wiring considerations Capacitive coupling Resistive coupling/ground loops Inductive coupling Systematic errors Imperfections of amplifier System noise floor Conclusion

IHP Im Technologiepark Frankfurt (Oder) Germany © All rights reserved Measurement System based on Agilent proposal SR570 low noise current preamplifier with Agilent 35670A dynamic signal analyzer

IHP Im Technologiepark Frankfurt (Oder) Germany © All rights reserved Wiring Problem – Capacitive Coupling

IHP Im Technologiepark Frankfurt (Oder) Germany © All rights reserved Wiring Solution – Capacitive Coupling Turn off noise source if possible, e.g. TFT screens Reduce stray capacitance by increasing distance to noise source Use a metal box for shielding

IHP Im Technologiepark Frankfurt (Oder) Germany © All rights reserved Wiring Problem – Resistive Coupling, Ground Loops

IHP Im Technologiepark Frankfurt (Oder) Germany © All rights reserved Wiring Solution – Resistive Coupling, Ground Loops Star configuration central ground point Use heavy ground bus to increase conductivity of ground connections

IHP Im Technologiepark Frankfurt (Oder) Germany © All rights reserved Wiring Problem – Microphonics Vibrations can change the cable capacitance due to small changes in geometry current is generated Ensure stable placement of equipment Use high quality cable

IHP Im Technologiepark Frankfurt (Oder) Germany © All rights reserved Wiring Problem – Inductive Coupling 1 Most critical for on-wafer measurements Occurs even if electrically isolated Is like a transformer with 1 secondary winding

IHP Im Technologiepark Frankfurt (Oder) Germany © All rights reserved Wiring Problem – Inductive Coupling 2 Disturbance depends on DUT conductivity Measurements of high conductive DUTs are most influenced

IHP Im Technologiepark Frankfurt (Oder) Germany © All rights reserved Wiring Solution – Inductive Coupling Turn off noise sources, e.g. coolers/heaters Minimized the area of the pick-up loop use twisted pairs cables Consider usage of RF probes (GS or GSG) no loop from coaxial cable minimal area for magnetic field

IHP Im Technologiepark Frankfurt (Oder) Germany © All rights reserved Wiring – on-Wafer Twist cables as good as possible Minimized pick-up loop area Usually coaxial cable does not shield magnetic fields

IHP Im Technologiepark Frankfurt (Oder) Germany © All rights reserved On-Wafer Wiring Example Central ground point Twisted triaxial cable

IHP Im Technologiepark Frankfurt (Oder) Germany © All rights reserved On-Wafer Wiring Considerations How many connections to protective earth conductor? Ground loop(s) if more than one Check wafer prober, SMU, signal analyzer, current amplifier Check triax/coax adapters if used Use only one central ground point RF probes are highly recommend

IHP Im Technologiepark Frankfurt (Oder) Germany © All rights reserved Recommendations Prevent loops in wiring twist cables use star configuration Use short, high quality cable Use RF probes (GS or GSG configuration) Place everything in a metal box use shielded wafer prober Switch off unnecessary equipment Is thermo chuck really necessary?

IHP Im Technologiepark Frankfurt (Oder) Germany © All rights reserved Systematic Errors 1 Imperfections of the current preamplifier Input resistance is not zero (depending on gain) Current compensation source has finite source impedance

IHP Im Technologiepark Frankfurt (Oder) Germany © All rights reserved Systematic Errors 2 Small signal equivalent circuits of DUT (MOSFET) and SR570 current amplifier input stage

IHP Im Technologiepark Frankfurt (Oder) Germany © All rights reserved Systematic Errors 3 3 paths for current flow Measured current is only a part of the noise current

IHP Im Technologiepark Frankfurt (Oder) Germany © All rights reserved Systematic Errors 4 R IN and R COMP are known from amplifier settings g OUT is derived from DC measurement Inoise can now be calculated

IHP Im Technologiepark Frankfurt (Oder) Germany © All rights reserved Systematic Errors 5 System noise floor and noise from compensation current source Compare with measured data with system noise

IHP Im Technologiepark Frankfurt (Oder) Germany © All rights reserved Example Measurement p-MOSFET at 2 different BIAS points VG=-1.2, VD=-1.2 VG=-0.9, VD=-1.2

IHP Im Technologiepark Frankfurt (Oder) Germany © All rights reserved Conclusion Current based noise measurement system was presented Potential wiring problems and solutions Guidelines for on-wafer wiring Imperfections of the measurement equipment System noise floor Example of noise measurement

IHP Im Technologiepark Frankfurt (Oder) Germany © All rights reserved 1/f Noise Measurements Thank you for your attention