rf in science and industry jonathan allen, ph.d. rf electronics consulting philadelphia conet

1

RF in Science and IndustryJonathan Allen, Ph.D.

RF Electronics Consulting

Philadelphia CONET

2

What is RF?

3

Maxwell

4

James Clerk Maxwell 1831-79

5

RF Vs. Pwr. or LF

• LF: System dimensions << so propagation times are insignificant within system.

• RF: Phase diff. due to propagation times.

• RF: Skin effect = (2/ o)1/2 [mks]

• In RF plasmas, ion and electron migration per 1/2 cycle generally << sys. Dimensions.

• Small L and C values much more important

6

LF Capacitors & Inductors

7

RF Capacitors & Inductors

8

ISM Bands (U.S.)

Center Freq. Bandwidth Availability

6.780 MHz 30 kHz Local acceptance*13.560 MHz 14 kHz Worldwide*27.120 MHz 326 kHz Worldwide*40.680 MHz 40 kHz Worldwide915.00 MHz 26 MHz Reg. 2 (Americas)2.45 Ghz 100 MHz Worldwide

9

Examples of ISM RF• Heating of lossy materials

– Plastic welding (PVC)

– Cooking

– Drying

– Glue curing

– Medical (diathermy, ablation, cautery)

• Materials testing

• NMR/MRI

• Plasma processes– Sputtering & deposition

– Etching

– Spectroscopy

10

RF HeatingPolar molecules flip orientation as e-field reverses. Some of the energy is dissipated as heat (dielectric loss).

11

RF Gluing (also plastic welding)

12

13

14

RF Drying

• Use for wood, foods, ceramic greenware

• Fast

• Selective--Heats only wet zones, uncured resins.

• Uniform in depth.

• Controllable – Reduce RF power as product approaches goal

• Often uses 27 or 40 MHz

15

RF Drying Wood

SAGARF-VacuumTimber dryingsystem

16

Drying Potato Chips

17

RF Induction Heating• Usually uses LF ~100 KHz for metals

• Localized heating possible Zone refining

• No combustion products or oxygen (can heat in vacuum)

18

Induction Heating Metal Rod

19

Lab Measurement

The same properties of polar molecules that enable RF heating also measure moisture content of wood, flour, etc. with an RF capacitance bridge.

RF induction coils measure the thickness of metallic films and foils based on skin-depth.

20

Plasmas Generate:

• Free electrons

• Positive ions

• Radicals

• Energetic particles

• Spallation of target (sputtering)

• Chemical reactions

• Excited atoms and molecules

• Light (glow discharge)

21

Paschen Curves--Breakdown vs. PressureMFP (cm) = 5x10-3/p (torr)

22

Plasma Sputtering

Energetic ions impact target and dislodge atoms ormolecules. These migrate to the substrate where they deposit to form a thin film.

Sputtering may be reactive, such as an aluminum target whose sputtered atoms reacting with oxygenin the process gas to form an Al2O3 film.

23

Plasma Sputtering

24

Plasma Etching

Plasma produces chemically active radicals which react with unmasked areas of wafer.This etches away material.

e.g. Fluorine radicals and ions etch silicon:

C F4 + e- C F3 + F + e-

Si + 4F Si F4

25

Plasma Etching with Mask

Plasma

Mask

RF

DC field superimposed on RF helps accelerate F- ions

26

Amorphous Si Plasma Deposition

SiH4 Si + 2 H2

27

ICP Spectroscopy

28

How to Generate RF

• Spark generator (obsolete, dirty)

• Power oscillator (efficient, cheap, but frequency not well defined)

• Oscillator (usu. xtal), driving Power amplifier (present industry standard)– Vacuum tubes– Bipolar transistors– Power FETs

29

Power Oscillator

30

Oscillator-Amplifier System

31

Power Tubes 4-400C, 5CX1500A

32

RF Power Transistor

33

Impedance Matching

RF generators conventionally have 50 (resistive) output impedance.

Loads can have any complex (and varying) impedance. Matching networks allow the generator always to see a 50 resistive load and therefore operate efficiently.

34

L Network

35

Pi Network

36

Univ. Matching Network, Can set as L or Pi

37

Allen Matching Network

38

Allen MN Physical Construction

39

RF Instrumentation

• Current measurement

• Voltage measurement– Broadband– Frequency selective

• Directional power

• Circuit analysis

40

RF Ammeter

41

RF Ammeter (Square-law scale)

42

Induction Ammeter

43

VTVM with HF Probe (hp 410C)

44

Calibrated Receiver (EMC-25)

45

Single Frequency Detector

46

Directional Wattmeter (Bird 43)

47

RF Impedance Meter (hp 4815A)

48

Grid Dip Meter (Measurements 59)

49

Important Uses of RF

• Food

• Construction

• Metallurgy

• Semiconductors (Discrete, IC, Photovoltaic)

• Optics

• Health and Medicine

• Laboratory science