orr michael golan alexander svetlitza karen...

Preformed By:

Orr Michael Golan

Karen Goldberg

1

Supervised By:

Alexander Svetlitza

Presentation Outline Project Objective

Theoretical Background

DC to DC Buck Converter

HFSS

Inductor Requirements

Modeled and Simulated Devices

Bondwires inductor with magnetic core

Magnetic materials

Skin depth effect

Conclusions

2

Project Objective Study and implement high performance bond wire MEMS

Inductors with magnetic cores, assess their performance

using the HFSS simulator, and measure the produced

inductors with Agilent impedance analyzer

3


A buck converter is a step-down DC to

DC converter.

Theory of operation:

• Closed state – The inductor stores

energy

• Open state - The inductor discharges the

stored energy

The output voltage is relative to the duty

cycle:

4

0

o i

D T T

V D V


HFSS is a high performance industry-standard

electromagnetic field simulator employing the

finite-element method and adaptive meshing for

arbitrary 3D volumetric passive device modeling.

It integrates simulation, visualization, solid

modeling and automation in an easy to learn

environment where solutions to 3D EM models are

quickly and accurately obtained.

5

Inductor Requirements Resistance:

Inductance:

Current:

Frequency Range:

6

0.3R

0.5L H

1I A

1 10 MHz


7

2L nH

4L nH

Getting Started & Sanity check – 1-

turn planar square spiral inductor

simulation

L Obtained:

L Expected:

Cause: Low number of turns


1 turn planar square Inductor with magnetic

material FeCoNi:

UnSimulatable!!

8

Modeled and Simulated Devices Straight inductor surrounded by slotted

magnetic materials FeCoNi & CoZrTa

Expected inductance according to article:

Inductance obtained in HFSS simulation:

9

3.8L nH

3.966L nH

Modeled and Simulated Devices Spiral inductor surrounded with magnetic

material CoZrTa

Expected inductance according to article:

Inductance obtained in HFSS simulation:

10

160L nH

198 200L nH

Modeled and Simulated Devices Naked spiral inductor – Magnetic field analysis

Edges appear to have the largest magnetic field

11

Modeled and Simulated Devices Meander matrix inductor – a direct application

of the naked spiral inductor results.

High Resistance, causing low Quality factor, and

too low Inductance

12

Modeled and Simulated Devices Counter-symmetry across inner circle

bond wires array, with magnetic material

Central loop containing high current over

small area, increases magnetic flux in the

middle

Geometry causing extremely

uniform field in the middle

of the array

13

Modeled and Simulated Devices Bond wires (BW) as an inductors with magnetic

cores

Properties:

2 mm outer diameter

1 mm inner diameter

0.3 um height

Magnetic core material

25-50[um] BW diameter

(Skin depth effect)

Either single or double BW loop

14

Magnetic Core Material Desired Properties:

High permeability for all frequencies in range

Low conductivity

Low magnetic losses

Compatible size

Two materials found compatible are ferrite #43

and ferrite #61 by “Fair-Rite”

15

Properties of Fair-Rite #43 ferrite

16

Properties of Fair-Rite #61 ferrite

17

Permeability modeled as complex number:

Real part responsible for B/H ratio

Imaginary part corresponds to power losses (Magnetic Losses)

Both are independent functions of frequency

Exact loss is geometry dependent. Generalization from

Maxwell's Equations:

This effect can be seen as a rise in resistivity as the

frequency grows.

Complex Permeability Effects

18

In AC regimes, current only partially permeate the

conductor through which it flows. It runs along the outer

shell and penetrates up to a skin depth of:

This effect could cause the effective area of conductance

(for resistance calculations) to be smaller than the

physical area - which would cause unnecessary losses in

the material.

2 7

1 1

4 10m

S f MHzm

Skin Depth Effect

19

The skin depth of gold, aluminum, and copper is:

We are interested in

gold and copper

Minimal skin depth

for both metals is 20-25 [um]

copper conductors are 100[um]x5[um] fully

permeated for all F no losses due to skin effect

In order to avoid these losses for all frequency

range, BW must have a diameter of up to 50[um]

Skin Depth Effect

20

D=25-50 [um] BWs using ferrite #43 Increasing BW diameter BW reduces series

resistance for all F only for

By expanding the diameter, the inductance decreases

by only 0.3%, whereas the resistance decreases by

62.5%!!!

21

50D m

Single or Parallel BWs?

22

Parallel resistors cause lower resistance than single

resistor

The higher the cross-sectional area is, the lower the

Resistance:

2

50 50 2

22

25 25

25 2

252

25

1 where D is the BW Diameter

2

For D=50 :

1

25

For 2 Parallel BW each with D=25 :

1

252 1

212 252

252

2

OneBW m D m

D m D m

Two Parallel BWs m

D m

Two Parallel BWs m O

RD

m

R R

m

R RR

R

R R

50ne BW m

Conclusions…

23

Toroidal inductor models are superior to planar models

for our set of requirements

With current magnetic material we cannot generate

enough inductance by using small inductors

Once a suitable magnetic material is found, optimization

is possible (and easy)

orr michael golan alexander svetlitza karen...

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