Woochul Jeon & John Melngailis

* RF Measurement & design: Todd Firestone & John Rodgers

•IC circuit design: Robert Newcomb

University of Maryland

Design, Fabrication, and Testing of On Chip Microwave Pulse Power Detectors

Motivation:

-- incident hostile RF radiation on electronics can cause most harm at the chip level

-- a way of measuring the level of the RF voltages induced on the most vulnerable sites is useful

-- conventional probing of the chip will disturb the measurement, so build the detector into the chip

Microwave pulse power detector

RF+

-DC

10pF 5kΩ

Schottkydiode

RF input:5GHz,2Vp_p

Output

-1.2

-0.7

-0.2

0.3

0.8

0 100 200 300 400 500Vin

(V)

200ns

0

0.05

0.1

0.15

0.2

0 100 200 300 400 500

Time (ns)

Vou

t (V

)

Pulse response time: 64nsec

Schottky diode model: - turn on voltage: 0.2V - Series resistance: 214Ω- Junction capacitance: 16fF

RF input is rectified by the Schottky diode and stored in the capacitor. RF pulse input is filtered to yield low frequency signal.

Three ways to make diode detectors on chips

- Post CMOS fabricated Schottky diode (FIB)

- CMOS process Schottky diode

- MOSFET used as rectifier

half wave rectifier

full wave rectifier

Focused Ion Beam milling and deposition(Post-CMOS fabrication, access to silicon)

• Maskless fabrication of devices by milling or depositing materials at any location

• Possible 3D fabrication by tilting the sample stage

FIB-Milled Circuit Cross SectionCircuit Rewiring: Cut and Jumper

Cross section a CMOS chip

Ion beam(milling)

e-beam (imaging)

M1M2M3

Pad

Via1μm

0.7μm

SiSiO2

6.8μm

52°

Fabrication of Schottky diode by FIB on a CMOS chip, etched down to metal-1

SiO2

Al

FIB milling

Pt by FIB deposition

Schottkycontact

• Cross section of burned out device after applying 8V of forward bias voltage• cut to disconnect ohmic contact

n-substrate contact - Ohmic

First cut for disconnecting ohmiccontact

Second cut & fill for Schottky contact

n+ diffusion and metal contact(Ohmic)

n-well

Al

Al

SEM image of a FIB processed diode(a) Milling silicon and Platinum deposition,(b) Cross section of the fabricated device: (c) Undercut by tilted FIB to minimize contact area

FIB Schottky diode fabrication

FIB Metal(Pt) deposition

Mill SiO2 to expose metal and Si layer for

contacting to pad

Metal layer connected to the pad for directly injecting RF signal

Start with a CMOS chip

Tilted (52°) FIB milling

52° tilted FIB milling from two sides for

undercut

Si n-well

Aln+

SiO2

FIB milling

Schottky contact

FIB milled cut for Schottky contact

Pt by FIB deposition

Schottkycontact

(a) (b)

(c)

SiO2Al

FIB Undercut

Al

Fabrication of Bridge shaped Schottky diode by FIB on a CMOS chip

RF pulse response of Bridge shaped FIB Schottky diode

Pulse response

0

0.5

1

1.5

2

2.5

3

0 2 4 6 8 10 12Time(usec)

Vou

t(V)

0

0.1

0.2

0.3

0.4

0.50.6

0.7

0.8

VinVout

Pulse response time: 170ns

1GHz, 15dBm RF pulse input

CMOS Schottky diodes• Standard CMOS process does not allow a Schottky contact

Modification requiredSkip n+ diffusion in metal to nwell contact area

SiO2

n+

p - Substrate

Al Al

Schottky Contact

Ohmic Contact

nwell

n+

Al

n+

p - Substrate

Al Al

Ohmic Contact

Ohmic Contact

nwell

n+

Al

n+ diffusion

Omit n+ diffusion

nwell-metal contact in Standard CMOS process

Modified nwell-metal contact (Schottky contact)

CMOS Schottky diodes

n+

p - Substrate

Al AlSiO2

Schottky Contact Ohmic Contact

nwelln+

Al

dd = 2μm to 30μm

Diode IV

-0.5

0

0.5

1

1.5

2

2.5

-0.5 0 0.5Vin (V)

Iout

(mA

)

I(30x30)I(8x8)I(2x2)

Ideal IV

100Ω

Series resistance

494Ω

6.5kΩ

Schottky contact

Ohmic contact

Cross-section

Alternative CMOS design(MOSFET diode)

DC Simulation and measured resultMeasured result: turn on voltage shift to –0.1V

Vout vs. Vin

-0.005

0.005

0.015

0.025

0.035

-0.5 0.5 1.5 2.5Vi(V)

Vo(

V)

VmeasuredVsimulated

RF pulse

M1

M2 M3

I1

I2 I3

Vin

Vo

R

Vx

C

Vdd

MOSFET diode power detector circuit

MOSFET detector circuit Full-wave rectifier circuit

1kΩ5pF

RF pulse

M1

M4

I1

I2

Vin

Vo

M3

M2

Vdd

Vss

M4

R

Iout

Vin

Vout

DC Simulation and measured resultMeasured result: turn on voltage shift to 0.2V

Full wave rectifier

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

-1.8 -1.2 -0.6 0 0.6 1.2 1.8Vin (V)

Iout

(mA

)IsimulatedImeasured

Measured result (Comparison)

Power sweep (-15dBm to 15dBm) at 1GHz

0

0.5

1

1.5

2

2.5

-15 -5 5 15

FIB Schottky diodepn Junction diode

Full wave MOSFET

CMOS Schottky diodes

Frequency sweep (1GHz to 10GHz) at 15dBm

0.1

1

10

1 2 3 4 5 6 7 8 9 10

FIB Schottky diodepn-Junction Diode

CMOS Schottky diode

Full wave MOSFET

Large diode

Comparison table

-1

16.5

4.91

192n

p-type 4μm2

n-type 1.4μm2

n-type 92μm2

-21

36

4.93

820n

CMOS diode

-19.5

34.5

2.05

776n

-10

25

2.44

101n

Full wave

MOSFET

Sensitivity (dBm)(smallest possible detection)

Dynamic range (dBm)

Frequency response(Vout at 1GHz / Vout at 10GHz)

Pulse response time (sec)

pnJunction diode

MOSFET detectorFIB diode

3-10-18-11-20.5

1225232625.5

27.44.439.593.973.14

16μ56n200n170n6 μ

1kΩLoad

150kΩLoad

Bridge 1μm2

n-type 15μm2

Best for short burst

Best for sensitivity & dynamic range

RF radiation test on a patch antenna structure

Horn structureRF radiation

12 cm10 cm

6 cm

12cm x 10cm x 6cm size box was used for radiation test

Output port

• Top viewGround plane

Bonding to ground plane Patch antenna

6cm6cm

RF radiation test result(Illustration of applications)

Working in the square law region, (Power level: output of the RF source)

Power density =

Power on a patch antenna (1500x750 μm2) ≈ Pin – 47dBm

2322

2

/106.110151

101566 cmPin

cmcmcmPin −×=

××

××

×

Vo vs. Freq. (at 40dBm)

0

5

10

15

20

9.5 11.5 13.5 15.5 17.5 19.5Frequency (GHz)

Vou

t(mV

)

Pin vs. Vout (at 12GHz)

0

20

40

60

80

100

120

25 35 45 55Power level(dBm)

Vout

(mV)

Pin

Detecting RF level at a PCB board

PCB board

IC 1 IC 2

IC 4

Input(RF pulse)

Output

Power detector

Power at node 1

Power detector

Power at node 2

Power detector

Power detector

Power detector

IC 3

IC 5

Power at node 3

Power at node 5

Power at node 4

Front sideBack side

Metal line connected to the detector

Schottydiode Detector

To oscilloscope

RF pulse Radiation test (x-band)-Detecting RF level at a PCB board

RF sourceAgilent 83731B Tektronics

TDS 620BOscilloscope

Amp

XBandHorn antenna

Anechoic chamber

Target

DC Probe Waveguide

Coaxial cable

RF pulse Radiation test-Measured result

Frequency sweep at 10dBm

0

0.01

0.02

0.03

9.2 9.6 10 10.4Frequency (GHz)

Vout

(V)

with antennano antenna

After measurement, antenna structure was disconnected Similar result for with or without antenna connection except around 10.2GHzThe metal line structure is tuned at 10.2GHz pulse signal

With antenna

Without antenna

Power sweep at 10.2GHz

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

18 23 28Power level (dBm)

Vout

(V)

Summary

• fabricated on-chip microwave pulse power detectors - FIB Schottky diodes as a post-CMOS process- Schottky diodes in modified CMOS process- MOSFET power detector circuits

• tested and evaluated diode RF detectors - using probes- RF incident on chip- RF incident on circuit board with chip

Future work & Challenge

• fabricate chips with built-in diode detectors and built in signal processing, to substitute for chips at vulnerable sites during tests

Synergistic activity:• harvesting of RF power for passive devices

- RFID tags- RFID tags with built-in sensors

(many applications: military logistics and monitoring, environmental, homeland security, medical…..)

Publications in Journals

W. Jeon, T. Firestone, J. Rodgers, and J. Melngailis, “Design and fabrication of Schottky diode, on-chip RF power detector”, Solid state electronics, Vol. 48, Iss. 10-11, pp. 2089-2093, Oct 2004

W. Jeon, T. Firestone, J. Rodgers, J. Melngailis, “On-chip RF pulse power detector using FIB as a post-CMOS fabrication process”, Electromagnetics, Vol. 26, Num 1, pp. 103-109, Jan 2006

W. Jeon and J. Melngailis, “CMOS and post-CMOS on-chip microwave pulse power detectors”, Solid state electronics, in press

ConferencesW. Jeon, T. Firestone, J. Rodgers, and J. Melngailis, “Design and fabrication of Schottky diode, on-hip RF power detector”, Proc., 2003 ISDRS, pp. 294-295, Washington DC, Dec. 2003W. Jeon and J. Melngailis, “CMOS & Post CMOS Fabrication of on Chip Microwave Pulse Power Detectors”, Proc., ISAP2005, Vol. 1, pp 221-224, Seoul, Korea, Aug. 2005W. Jeon, T. Firestone, J. Rodgers, J. Melngailis, “CMOS/post-CMOS fabrication of on-chip Schottky diode microwave pulse power detectors”, Proc., DET&E conference, Albuquerque, New Mexico, Aug. 2005W. Jeon, J. Melngailis, and R. W. Newcomb, “CMOS passive RFID transponder with read-only memory for low cost fabrication”, Proc., IEEE SOCC 05, pp. 181-184, Washington DC, Sept. 2005W. Jeon and J. Melngailis, “CMOS&post CMOS on-chip microwave pulse power detectors” Proc., 2005 ISDRS, Washington DC, Dec. 2005W. Jeon, J. Melngailis, and R. W. Newcomb, “CMOS Schottky diode microwave power detector fabrication, Spice modeling, and application”, IEEE Intl. Work. Electronic Design, Test, & Applications (DELTA 2006), pp 17-22, Kuala Lumpur, Malaysia, Jan. 2006W. Jeon and J. Melngailis, “On-chip CMOS microwave pulse power detectors”, 2006 IEEE Power Modulator Conference abstracts, pp 64-65, Washington DC, May 2006

Related, e.g. RFIDW. Jeon, J. Melngailis, and R.W. Newcomb, “Disposable CMOS passive RFID transponder for patient monitoring”, IEEE ISCAS, pp 5071-5074, Island of Kos, Greece, May 2006M. Moskowitz and W. Jeon, “Design of Portable integrated Diode-Based Biosensor for diabetic diagnoses”, World Congress on Medical physics and Biomedical engineering, Seoul, Aug. 2006, acceptedW. Jeon and J. Melngailis, “CMOS Schottky diode for photo-detector and thermal detector applications”, IEEE sensors, Oct 2006, accepted

RF pulse Radiation test-Measured result

• Antenna gain: The ability to focus radio waves in a particular direction(dBi : decibels relative to isotropic)

For 0.0302V output at 10.2GHz, -2.8dBm direct injection needed

2

2216λ

π

TxTx

RxRx GP

LdPG =Frequency Power [dBmwith antenn

10 30 0.003410.05 30 0.004210.1 30 0.0094

10.15 30 0.026810.2 30 0.0302

10.25 30 0.013410.3 30 0.0128

10.35 30 0.010410.4 30 0.0056

10.45 30 010.5 30 0.0018

10.55 30 0.001810.6 30 0.0016

Frequency Power Vout10 -6 0.004810 -5.5 0.005210 -5 0.01410 -4.5 0.014410 -4 0.027610 -3.5 0.01610 -3 0.020810 -2.5 0.043610 -2 0.052410 -1.5 0.06810 -1 0.073610 -0.5 0.084810 0 0.0992

Radiation Direct injection

30dBm radiation made the same output voltage as -2.8dBm direct injection

PTx = 30dBm (Radiated power)PRx = -2.8dBm (Received power)

d = 1cm (distance b/w antenna and target)GTx = 23.28 dB (Horn antenna gain)L = 1 (system loss factor, assumed)λ = 2.96cm (wave length)

GRx = -43.53dBi

FIB milling

Target material

Focused ion beam column

Sputtered ion, molecules, atoms

Ion column focused on the location to be milled. Atoms, electrons, and molecules are sputtered from the target material

FIB ion induced deposition

Ion column focused on the location for deposition. Similar to Chemical Vapor Deposition.

Focused Ion beam

Deposited material

Target material

Desorbed reaction products

Precursor gas

Precursor gas feed needle

Adsorbed precursor gas in mono-layer