Schottky Diode and MOSFET RF-Detector and Focused Ion Beam Post-Processing

MURI Annual Review

Woochul Jeon, Robert Newcomb Todd Firestone, John Rodgers

& John MelngailisUniversity of Maryland.

Original Project Objectives:

- Direct analog microwave level measurement on a chip(goal: up to 100GHz) using

a) Schottky diodesb) Thermal detectors

- Incorporation of RF detectors on chips, including FIB diode fabrication on existing chips

- Focused ion beam diagnosis circuit restructuring and device diagnosis by burned out element sectioning

Changes to Objectives:- Thermal detectors not pursued- Concentrate on lower frequency <10GHz- MOSFET power detectors included

Outline

• Operation of Schottky power detector• Fabricated Schottky diodes by CMOS process• Fabricated Schottky diodes by FIB as a post

CMOS process• MOSFET power detector• Effect on adding power detector to a logic circuit • Conclusion and future work

RF+

-DC

Operation of RF Power Detector

50pF 1kΩ

100ns

1.5V

0V

-1.5V

250mV

-20mV

RF input

Output

0s 100ns 200ns 300ns 400ns

Design a diode structure to minimize series resistance of n layer without using Silicon Molecular BeamEpitaxy(Si-MBE)

Minimize contact spacing

Schottky diode Design for CMOS process

n+2um

n - Substrate

Al AlSiO2

Schottky Contact Ohmic Contact

N+ doped area

Al

SiO2

FIB milling (2µm x 3 µm)

FIB Pt deposition

2µm scale 20µm scale

Fabrication of Schottky diode by FIB

RF direct injection test measurement setup

RF sourceAgilent 83731B

TektronicsTDS 620BOscilloscope

Cblock

Schottky diode Power detector

Cascade GSG probe150µm pitch

DC output vs. Pow er level

0

0.5

1

1.5

2

2.5

0 5 10 15 20

Pow er [dBm ]

Vout

[V]

5 GHZ 6 GHZ10GHz FIB 8GHz FIB

Frequency sweep

0.1

1

10

1 2 3 4 5 6 7 8 9 10Frequency(GHz)

Vou

t(V)

FIB CMOS compatilbe diode

Vout vs. Frequency sweep Vout vs. RF power sweep

RF direct injection test of evaporated contact diode and FIB diode made at UMd

(2µm x 3 µm contact area,)

• Schottky contact could not be made on CMOS process, though it depends on CMOS run itself.

• We have tried 4 times with different CMOS process. However, no Schottky contact was made.

Post CMOS process required

Photo of diode structure with test pads for Cascade probe made by MOSIS CMOS process

Schottky contactContact area: 2x2 µm2 - 40x 40 µm2

Ohmic contact

diode

100 µm

150 µm

Cross section a CMOS chip

Ion beam(milling)

e-beam (imaging)

M1M2M3

Pad

Via1µm

0.7µm

SiSiO2

6.8µm

52°

Fabricating Schottky diodes on CMOS chip by FIB

n substraten+

SiO2 Al

n

Al

FIB milling

n

Al

FIB Metal(Pt) deposition

Schottky contact

Mill SiO2 to expose metal layer for contacting to pad

To pad for directly injecting RF signal

Start with a CMOS chip

Fabrication of Schottky diode by FIB on a CMOS chip

SiO2

Al

FIB milling

Pt by FIB deposition

Schottky contact

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

p-substrate contact - Ohmic(Supposed to be Schottky contact)

First cut for disconnecting ohmiccontact

Second cut & fill for Schottky contact

n+ diffusion and metal contact(Ohmic)

n-well

FIB diode IV curve(log scale)

1.0E-09

1.0E-07

1.0E-05

1.0E-03

1.0E-01

1.0E+01

-10 -5 0 5

Vin(V)

Iout

(A)

FIB diode IV curve(-1V to 1V)

-3

0

3

6

9

12

15

18

21

24

-0.8 -0.4 0.0 0.4 0.8

Vin(V)

Iout

(uA

)

Measured result(DC)

Measured result (Power sweep)

0

0.5

1

1.5

2

2.5

-20 0 20

Pow er level(dBm )

Vout

(V)

1GHz

3GHz

5GHz

0

0.05

0.1

0.15

0.2

0.25

0 10 20

Pow er level(dBm )

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 10 20

Pow er level(dBm )

Power sweep at 1GHz, 3GHz, and 5GHz for three diodes: n-type 15µm2

diode, 6µm2 diode, and p-type 4µm2 Schottky diode, respectively

Frequency sw eep(1 to 15GHz) at 15dBm

0.01

0.1

1

10

1 3 5 7 9 11 13 15

Frequency(GHz)

Vout(V)

Measured result (Frequency sweep)

Frequency sweep from 1GHz to 15GHz at 15dBm

n-type 15µm2

n-type 8µm2

p-type 4µm2

Alternative CMOS design(MOSFET diode)

MOSFET diode power detector circuit, Pspice simulation result, and layout

150kΩ ,1k Ω5pF

RF pulse

M1

M2 M3

M4

Vbias

Bias circuit

M5Vout

100mV

-100mV

330mV

310mV

2GHz, 0.1Vpp, 3µs pulse width

12.5mV

8us 10us 12us 14us

MOSFET diode measured result(Vin vs Vo curve)

Vin vs Vout

-5

-4

-3

-2

-1

0

1

-5 -4 -3 -2 -1 0 1

Vin (V)

Vout

(V)

Negative detectors.

• Detector with 1kΩ load • Detector with 150kΩload

V3

-1000-800-600-400-200

0200

-2 -1 0 1 V in(V )

Vo

(mV

)

RF direct injection test measurement setup

RF sourceAgilent 83731B

TektronicsTDS 620BOscilloscope

Cblock

MOSFET Power detector

DC bias

Cascade GSG probe150µm pitch

Frequency sweep

1.0E-03

1.0E-02

1.0E-01

1.0E+00

1.0E+01

1 3 5 7 9 11 13 15Frequency(GHz)

Vou

t(V)

0

0.2

0.4

0.6

-20 -15 -10 -5 0 5 10 15

Vo

ut

(V)

• Power sweep from –20dBm to 15dBm at 1GHz, 3GHz, and 5GHz

• Frequency sweep from 1GHz to 15GHz

• Pulse response time was 56 to 104nsec (1kΩ load) and 200 to 700nsec (150kΩ load) to –5 to 5dBm at 1 to 5GHz pulse

MOSFET detector measured result(RF direct injection with 1kΩ & 150kΩ load)

1GHz3GHz

5GHz

5dBm (150kΩ)

0dBm (150kΩ)10dBm (1kΩ)

5dBm (1kΩ)

0dBm (1kΩ)

150 k Ω

1 k Ω

Power sweep Frequency sweep

Vou

t(V)

dBm

Frequency sweep

0.01

0.1

1

10

1 3 5 7 9Frequency

Vout(V)

Power sweep (0dBm to 15dBm )

0

0.5

1

1.5

2

2.5

-15 -10 -5 0 5 10 15Power level(dBm )

Vo

ut(

V)

RF direct injection test for pn Junction diode(black line) and diode connected MOSFET(red line)*Green line: FIB Schottky diode power detector*Blue line: MOSFET power detector circuit for comparison

Better frequency response and sensitivity

Comparison of FIB diodes, pn junction diode & MOSFET detector with & without bias

MOSFET PD ckt.

Junction diode

MOSFET

Junction Diode at 10dBm

MOSFET at 10dBm

MOSFET PD ckt(150kΩ) at 5dBm

FIB Schottky diode(big)

FIB Schottky diode(Big) at 15 dBm

FIB Schottky diode(small) at 15 dBm

MOSFET PD (1kΩ) at 10dBm

Frequency sweep

Frequency (GHz)

Comparison table

Junction diode

MOSFETMOSFET detectorFIB diode

7dBm4dBm-12dBm-12dBm0dBm5dBm-10 dBmSensitivity(smallest possible detection)

> 10dBm> 10dBm25dBm15dBm> 15dBm> 15dBm> 25 dBmDynamic range

14.45.502.285.232.401.341.52Frequency response(Vout at 1GHz / Vout at 10GHz)

16µsec1.2µsec56nsec200nsec192nsec2.56µsec6µsecPulse response time

1kΩLoad

150kΩLoad

P-type 4µm2

N-type 6µm2

N-type 15µm2

Short pulse (< 1 µs) detection: MOSFET detector or small p-type FIB diode detector due to its fast pulse response time

Long pulse (>10 µs) detection: big n-type FIB diode is the best choice due to its flat frequency response, wide dynamic range, and good sensitivity

Effect on adding diode power detectors to a logic circuit

A

B

C

D

AB + CD logic circuit Series diode detector Parallel diode detector

Effect on adding diode power detectors to a logic circuit

Change output value when clock frequency becomes higher

With series diode With parallel diode Without detector

Low clock frequency (10MHz) High clock frequency (1GHz)

Effect on adding MOSFET power detectors to a logic circuit

A

B

C

D

AB + CD logic circuit Power detectorShowed a small delay, almost the same

With power detectorWithout detector at 1GHz

MOSFET detector circuit (Future work)Full-wave rectifier circuit

RF pulse

1kΩ5pF

M1 M2

Vi

Vo

M3 M4

M5 M6

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

-10 -5 0 5 10

Vi

Vo

Simulation result (Vi vs Vo, DC)

Detecting RF level on 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

Summary

• Schottky diodes were attempted by AMI 1.5µ, 0.5µ, and 0.35µ CMOS process through the MOSIS

• Schottky diodes were fabricated by FIB techniques on a CMOS chip and tested up to 15 GHz

• As an alternative CMOS design, MOSFET power detector circuit designed and tested

• pn junction diode and diode connected MOSFET detector tested and compared

• Schottky diode RF detector loading of logic circuit simulated

Publications:

Woochul Jeon, Todd M. Firestone John C. Rodgers, and John Melngailis,

“Design and fabrication os Schottky diode, on-chip RF detectors”

Solid State Electronics 48, 2089 (2004)

Woochul Jeon, Todd M. Firestone John C. Rodgers, and John Melngailis,“On-chip RF power detector using focused ion beam as a post-CMOS

fabrication process” to be published Electromagnetics Journal

Future work

- design (and implement) RF pulse detectors for system board,

- design (and implement) RF pulse detectors inside chips,

- build full wave rectifier circuits

- alter circuits with FIB

- test sensitivity of RFID tags to deprogramming with RF bursts (seeking industry funding)