Contact free potential mapping by vibrating capacitor Mizsei, János 1-4/10/2006 Laulasmaa Budapest University of Technology and Economics, Department of Electron Devices

Outline Introduction: potentials in general Do we really need contacts ?Ideal (static) voltmeter. Do we really need contacts ? What is it for ? Applications... …extension of the application (x-y scanning, higher resolution, (Kelvin Force microscopy) etc... Summary

Introduction: the potential working ability of a point charge in r the electric field: force on the charge it is a general „boundary condition” in the electronics electrochemical potential: advantages: it can be easily measured in a broad range, excellent for characterisation of physical systems:

VOLTMETERS ”Handy” voltmeters: 20 M  Electrometers: (?) (electron tubes, FET) Compensation: voltage measurements without current …without current. Do we really need contacts ?

The ideal VOLTMETER: R in =  How can we do that in practice? Capacitive coupling + compensation: „Vibrating reed voltmeter”

”Vibrating reed” voltmeter: static capacitive coupling: it is not applicable to transfer the information about DC voltage (except: MOS FET)static capacitive coupling: it is not applicable to transfer the information about DC voltage (except: MOS FET) solution: non-static (vibrating) capacitorsolution: non-static (vibrating) capacitor R=  Phase sensitive frquency selective current detector He

What else? Potential directly from the surface, without contact. Phase sensitive frequency selective current detector

The CPD: zero electric field between the plates ! CPD compensated: Lower work function (electron emission, positive surface charge) Higher work function (negative charge on the surface A B

Current to be detected: Capacitance: Charge:

Up to date equipment: frequency selective amplifying, phase sensitive (multiply) demodulation feedback of the DC voltage (automatic compensation) optical excitation for surface photovoltage measurements digital realisation second harmonics detection and feedback for distance control surface mapping (x-y scan).

V V cpd Tip vibration due to voltage on the tip: …stops when !!! Kelvin Force Microscopy: AFM + Kelvin

Photograph and CPD map of a printed circuit board sample Histogram (distribution of the CPD values) after wet polishing process

Surface potential map from biased thick film circuit Sections of the potential maps 0 V5 V 0 V 5 V Histogram (distribution of the CPD values) 0 V 5 V 0 V

Surface potential maps plotted from the silicon chips Vibrating tip over a silicon slice B E „dark” - „light” = potential barrier 4 mm

Potential maps from a CIGS (copper-indium-gallium- diselenide) thin film photovoltaic device „dark” - „light” = potential barrier

The effect of the external bias on a CIGS (copper- indium-gallium-diselenide) thin film photovoltaic device - = - = 20 V 0 V

Microscopic charges on SiO 2 surfaces by Kelvin force microscopy 100 nm native oxideoxide Si: P type,, 10 ohmcm

11:30:29 AM Fri Aug :11:07 PM Thu Aug V V

Micro domain potentials from gas sensor surfaces: agglomerated Ag on SnO 2 E~ V/m

Micro domain potentials from gas sensor surfaces: Au on SnO2

ALE SnO 2 layers: CPD and resistance maps 33K 30K 46K K 48K 133K K 71K K K  M 182 Chemical pictures by vibrating capacitor

Selective chemical sensing with potential mapping  360K  460K Material gradient Temperature gradient PdAgAuPtV SnO 2

Summary Vibrating capacitor methodVibrating capacitor method Examples: analytical tool and sensor (chemical signal converter)Examples: analytical tool and sensor (chemical signal converter) Conclusion: a lot of useful application possibilitiesConclusion: a lot of useful application possibilities