Design and optimization of Schottky diodes in CMOS

technology with application to passive RFID systems

Auto-ID lab Adelaide

Overview

• Introduction.• Design and layout of Schottky diode.• Modelling of designed SBD.• Applications.• Fabrication and measurements.• Conclusion.

The General RFID Idea

Normally a very weak reply is obtained

The black spot

Example Applications

• What can you do with this technology ?

Supply chain benefits– Reduce out of stocks, reduce inventory, speed up

delivery, check freshness, track and trace, produce to demand, identify sources of diversion, identify counterfeiting, theft prediction, faster recalls

Consumer benefits– Direct order from home, smart appliances, (e.g.

microwave, washing machine, refrigerator), smart healthcare, assisted living

New and less expected benefits– Customized products, smart recycling, checkout-less

stores

Passive RFID

• RFID tag chip in standard CMOS technology.

Low size.

Low cost.

Integration with existing logics and other modules.

• Supply sufficient operating power• Metal directly deposited on N-Well.• Titanium-Silicon/Tungsten-Silicon contact• Functional but needs more improvements.

Fabricated through MOSIS

Cross Sectional view of SBD

• Design a diode structure to minimize series resistance of n-well.

Cross Sectional view of SBD

Equivalent circuit

Multi-finger Schottky contact

• Reducing the series resistanceIncreasing the perimeter

Decrease junction capacitance

Prototyped SBD sizes

NoArea(squa

re Pico-meter

Perimeter (Micro-meter)

FingersContact

Dimension (um*um)

SD1 0.23 1.92 1 0.48x0.48

SD2 0.23 1.92 1 0.48x0.48

SD3 1.49 7.20 1 0.48x3.12

SD4 16.12 72.90 6 0.48x5.6

SD5 14.4 60.96 1 0.48x0.30

RFID Ant Model & Matching

• Start from dipole antenna model• Use the model from “Modeling And Simulation of A Dipole

Antenna for UWB Applications using equivalent spice circuits” John F.M. Gerrits, etc. Centre Suisse d'Electronique et de Microtechnique SA (CSEM) Neuchâtel – SWITZERLAND

+VTX-

Rs

R1 C2

C1 Rl

Rr

L1

+Vrx-

Rrad

+

V(Rrad)

-

0

source antenna

Matching and Optimal Input Level

• Equivalent circuit of RFID chip

• Vrx value for 73 (half wavelength dipole) radiation resistance at 150uW input

• 50 resistor voltage swing

Rs jXs

VuWRPV rpprx 296.0731502222)(

VuW

RR

RRPV

rload

loadrppload

120.05073

507315022

22)(

Matching and Optimal Input Level (Cont.)

• Quality factor of the RFID circuit (Serial configuration)

• Maximum voltage swing across the RFID chip• 150uW input would have a 0.7V Vp-p input

No other rectifier structure will work except Schottky diode rectifier structure

• Hard to decrease the input capacitance to increase the Q

Rs

XsQ

QRR

RRPV

sr

srpp

22

Rectifier circuit (SBD application)

SBD Rectifier layout

Measurement Plan

• Discrete SBD testGSD probing pads for de-embeddingS parametersDC parameters

• SBD rectifier testInput impedanceMatching circuit/boardAntennaReader/Signal generator and

PA+Antenna; Optimised tag

Discrete SBD Test

Prototype Reader

Future Work

• Test and extract the model parameters• Validating the SBD model• Improve the quality factor of the SBD• Increase reverse direction breakdown

voltage by guard ring (fabricated version dose not have)

• Improve efficiency by reducing parasitic capacitance

• Better impedance matching capabilities

Q&A

• Thank You