Expanding Impedance Measurement to Nanoscale:

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Aubrey Little
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1 Expanding Impedance Measurement to Nanoscale: Coupling the Power of Scanning Probe Microscopy with Performance Network Analyzer (PNA) Hassan Tanbakuchi Senior Research Scientist Agilent Technologies Agilent E Seminar Page 1

2 Outline SCM Basics. Microwave Network Analyzer Basics (VNA). Challenges of VNA as a SMM measurement engine. Addressing the measurement challenge. Electromechanical coupling challenge and solution Mechanical design. DPMM (Dopant Profile Measurement Module) System overview. Some interesting images. Page 2

3 Traditional SCM VCO Detector Scanning only qualitative poor sensitivity limited Atoms/cm3 No Conductors/Insulators dv dc Page 3

4 Network Analyzer Basics Page 4

forward and reverse reflection and transmission responses (S-parameters) of RF and microwave components Quantify

5 What is a Vector Network Analyzer? Vector network analyzers (VNAs) Transmission Are stimulus-response test systems Reflection S 12 Characterize forward and reverse reflection and transmission responses (S-parameters) of RF and microwave components Quantify linear magnitude and phase Are very fast for swept measurements Provide the highest level of measurement accuracy RF Source DUT S 21 S 11 S 22 Phase Magnitude R1 LO R2 A B Test port 1 Test port 2 Page 5

6 Lightwave Analogy to RF Energy Incident Transmitted Reflected Lightwave DUT RF Page 6

7 Transmission Line Terminated with Zo Zs = Zo Zo = characteristic impedance of transmission line Zo V inc Vrefl = 0! (all the incident power is absorbed in the load) For reflection, a transmission line terminated in Zo behaves like an infinitely long transmission line Page 7

8 Transmission Line Terminated with Short, Open Zs = Zo Vinc Vrefl In-phase (0 o ) for open, out-of-phase (180 o ) for short For reflection, a transmission line terminated in a short or open reflects all power back to source Page 8

9 Transmission Line Terminated with 25 Ω Zs = Zo ZL = 25 Ω V inc Vrefl Standing wave pattern does not go to zero as with short or open Page 9

10 High-Frequency Device Characterization Incident R Reflected A Transmitted B REFLECTION TRANSMISSION Reflected Incident = A R Transmitted Incident = B R SWR S-Parameters S 11, S 22 Reflection Coefficient Γ, ρ Return Loss Impedance, Admittance R+jX, G+jB Gain / Loss S-Parameters S 21, S 12 Transmission Coefficient Τ,τ Insertion Phase Group Delay Page 10

11 Standard Vector Network Analyzer as a reflectometer Source A/D S 11 LO Z = Z L L A Z + Z 0 0 k Ω B LO A/D Probe Very small capacitor High SNR Low Resolution Highly resistive load High SNR Low Resolution Load close to 50 Ohms Low SNR High Resolution Figure 1: reflection coefficient vs.. impedance Low resistive load High SNR Low Resolution Page 11

12 Proposed solutions Cancellation (Nulling) of the reflected wave can be done either in the RF front end or the IF stage: RF techniques: 1) Balun and amp 2) Differential Amp Source Extreme Load Impedance a1 b1 Ref-In Diff Amp Variable Attenuator Delay line Balun Amp A-in Page 12

13 Fully Automated Proposal System drift correction via ECAL Phase shifting and Attenuation are done through DSP Low IF frequency, and High speed ADC are chosen to minimize the computational round off error in DSP. Source ECAL DUT LO1 A B LO1 LO2 10 KHz IF LO2 10 KHz IF A/D1 + - DIF1 - DAC DSP1 DSP2 DAC + U93 A/D A/D High resolution amplitude tweaker Page 13

14 Simplified Single Frequency Solution Source LO A B LO Half wave length Coaxial resonator 50 Ohm A/D A/D Probe m1 freq= 1.910GHz S(1,1)=0.001 / impedance = Z0 * ( j0.003) 0 m2 freq= 1.910GHz db(s(1,1))= S(1,1) m1 db(s(1,1)) m freq, GHz freq (500.0MHz to 3.000GHz) Page 14

15 Electromechanical coupling Balanced Pendulum: How Does It Work Laser tracking spot remains fixed relative to Z-piezo & AFM cantilever Z-piezo does not bend Y scan Tube Design Pendulum Design Page 15

16 Early Design Suffers from Abrupt Localized Bend of Coax Connecting TIP to Diplexer Load Diplexer RF to PNA Scanner head With Conductive Tip Coax from the Tip to diplexer Page 16

Looped cable Looped cable Half Wavelength Cable Diffusion of

17 Distribution of Electromechanical Coupling Through Coaxial Loop Conductive Tip Conductive Tip Extraction tool Diplexer 50 Ohm CKT Looped cable Looped cable Half Wavelength Cable Diffusion of electrical/mechanical coupling with integration of enhanced VNA and Precision Machining Page 17

18 Speedy Conductive Tip Replacement RF Connection Pt/Rb Cantilever Alumina Carrier Conductive Tip Magnetic Jaw Page 18

19 DPMM Dopant Profile Measurement Module DPMM approach: Use the Flatband transfer function that is function of dopant density ( variable capacitor) that can be used as an AM mixer to modulate the reflected MW signal at the rate of Flatband drive frequency (<100 KHz). The said AM modulation index is function of the dopant density. Page 19

20 DPMM Block Diagram/Physical Realization Source Out CPLR Thru Source A CPLR OUT LO Half wave length Coaxial resonator 50 Ohm Signal IN A/D AMP Probe AMP AMP AMP dopant B AMP RCVR IN DPMM LO A/D Signal out To Lock in Page 20

21 DPMM Internal Structure and as an add on Module to PNA DPMM PNA PORT1 DPMM Internal MIC detail DPMM as an add measurement module to PNA Page 21

RF signal is reflected from the tip and measured by the Analyzer.

22 System Overview Photodetector Coaxial cable Coaxial Resonator Sample Sample scanning AFM in X and Y and Z (closed loop) The MW diplexer Ground/Shield Network Analyzer Network analyzer sends an incident RF signal to the tip through the diplexer. RF signal is reflected from the tip and measured by the Analyzer. The magnitude and the phase of the ratio between the incident and reflected are calculated Apply a model to calculate the electrical properties AFM scans AFM moves tip to specific locations to do point probing Page 22

23 SRAM Image Page 23

24 Page 24

25 Scanning only qualitative poor sensitivity limited Atoms/cm3 No Conductors/Insulators Page 25

Network Analysis Basics

Network Analysis Basics Adolfo Del Solar Application Engineer adolfo_del-solar@agilent.com MD1010 Network B2B Agenda Overview What Measurements do we make? Network Analyzer Hardware Error Models and Calibration Example Measurements