1Wolte3, June 24-26, 1998

Dipartimento di Fisica dell'Universita' and Istituto Nazionale di Fisica Nucleare, 20133 Milano, Italy.

* presently at: Silena International, 20063 Milano, Italy

The SuperFET: A High-Performance GaAs Voltage-Controlled Current Source for Cryogenic Applications

D.V.Camin, G.Pessina, E.Previtali and P. Ramaioli*.

OUTLINE:

EXPERIMENTAL MOTIVATION AND SPECIFICATIONS;

CONSIDERATIONS ON THE PREVIOUS SOLUTION;

TECHNOLOGICAL ASPECT;

DESIGN SOLUTION OF THE NEW TEST VERSION;

EXPERIMENTAL RESULTS;

SUMMARY.

2Wolte3, June 24-26, 1998

EXPERIMENTAL MOTIVATION AND SPECIFICATIONS

THE EXPERIMENT IS LOCATED AT THE LARGE HADRON COLLIDER AT CERN, IN GENEVA.

A VERY HIGH ENERGY BEAM OF PARTICLE WITH ENERGY IN THE TeV REGION WILL CROSS THE DETECTOR HAVING A LIQUID ARGON TANK AS THE REVEALING MEDIUM;

INCIDENTBEAM

TOP

VIE

W

LIQUID ARGON

WHILE CROSSING THE LIQUID, PARTICLES CREATE IONIZATION INSIDE ARGON;

THE APPLICATION OF AN ELECTRIC FIELD ALLOWS TO COLLECT THE CREATED CHARGES;

THE SEGMENTATION OF THE SPACE INSIDE THE LIQUID ALLOWS TO GET INFORMATION ON THE POSITION OF THE CREATED CHARGES AND IT SERVES ALSO FOR THE OPTIMIZATION OF THE CHARGE TRANSFER BETWEEN THE DETECTOR AND THE PREAMPLIFIER;

- HV

A CURRENT SENSITIVE PREAMPLIFIER WILL READ-OUT THE CURRENT GENERATED BY THE ELECTRONS.

EQ

UI.

CIR

CU

IT

3Wolte3, June 24-26, 1998

CONSIDERATIONS ON THE PREVIOUS SOLUTION (A)

THE TYPICAL SIGNAL SHAPE IS A TRIANGLE OF ABOUT 400ns TIME LENGTH.

THE MAXIMUM ENERGY IS EXPECTED TO CREATES A CHARGE GIVING RISE A SIGNAL CURRENT OF ABOUT 8mA.

8mA

400ns

430Ω

3.5V

A FIRST CURRENT SENSITIVE PREAMPLIFIER ABLE TO MEET THESE SPECS. HAS BEEN REALIZED AND TESTED.

THE PREAMPLIFIER CONSISTED IN A GaAs MESFET MONOLITHIC INTEGRATED CIRCUIT.

THE DYNAMIC OF THE PREAMPLIFIER WAS ABOUT 3.5V, LIMITED BY TO THE BREAKDOWN OF THE MESFETs TRANSISTORS USED.

A RELATIVELY SMALL FEEDBACK RESISTANCE WAS THEN USED TO MANAGE THE LARGE SIGNAL EXPECTED.

THE SMALL VALUE OF THE FEEDBACK RESISTANCE LIMITS THE FINAL ENERGY RESOLUTION DUE TO ITS ASSOCIATED PARALLEL NOISE, INVERSELY PROPORTIONAL TO ITS VALUE.

4Wolte3, June 24-26, 1998

RESULTSSLEW RATE 160 V/μsSWING (WITH 100Ω LOAD) 3.5VPOWER DISSIPATION 66 mWSERIES WHITE NOISE 0.32 nV/√Hz1/f NOISE COEFFICIENT Af ≈1-13 V2

DISPERSION OF THECHARACTERISTIC (500SAMPLES)

≈5 %

CONSIDERATIONS ON THE PREVIOUS SOLUTION (B)

= ONE COMPLETE PREAMPLIFIER

THE MESFET INPUT DEVICE HAS AN AREA OF LG x W = 3 x 24000 μm2.

TWO PREAMPLIFIERS ARE ACCOMMODATED ON A SINGLE CHIP

THE PREAMPLIFIER IS COMPOSED OF ONLY n-TYPE MESFET TRANSISTORS.

* IEEE TR. NUCL. SCIE. VOL.43, p.1649 (1996)NIM VOL. A395, p.134 (19997)

*

0,1

1

10

100

10 4 10 5 10 6 10 7 10 8

Ser

ies

Noi

se D

ensi

ty [n

V/H

z]

Frequency [Hz]

0.58 0.32

LPM

NM

White Noise

T = 87 K

5Wolte3, June 24-26, 1998

TECHNOLOGICAL ASPECT

THIS FIRST PREAMPLIFIER USES ONLY THE D-TYPE MESFETs HAVING THE LOWER NOISE IN THE MONOLITHIC PROCESS SELECTED (TriQuint).

AC REGION OF INTEREST

DC REGION OF INTEREST

Type of FET M D ETemperature 300 K 77 K 4 K 300 K 77 K 4 K 300 K 77 K 4 K

Threshold voltage [V] -2.9 -2.0 -1.8 -1.1 -0.8V -0.7 +0.05 +0.35 +0.45Max. D-S op.

voltage [V] 4.0 3.0 ~2.0 5.0 4.0 ~3.0 15 12 8

1/f factor Hf =AfCiFET[10-26 Joule] n/d 76 n/d n/d 10 2.8 n/d 100 n/d

WE THEN STARTED TO USE THE E-TYPE MESFET, LOCATING IT IN CIRCUIT POSITIONS WHERE ITS NOISE IS NOT REFLECTED AT THE INPUT, BUT THE DYNAMIC VOLTAGE EXCURSION IS EXPECTED TO BE LARGE.

BUT THE PROCESS HAS AVAILABLE 2 MORE TYPE OF MESFETs, WITH DIFFERENT DOPING LEVEL, UP TO NOW NOT CONSIDERED FOR THEIR LARGE 1/f NOISE.

THE E-TYPE, IN PARTICULAR, IS THE ONE HAVING THE LOWER DOPING PROFILE, WITH A THRESHOLD VOLTAGE SLIGHTLY POSITIVE.

400kV/cm E

,2qN

E V

BR

D

2BR

BR

≈

=εOWING TO THEIR DOPING LEVEL,

THE D-TYPE MESFETs, HAVE A RELATIVELY LOW BREAKDOWN VOLTAGE WHICH HAS LIMITED THE VOLTAGE EXCURSION OF THE PREAMPLIFIER.

316D donors/cm 104 N ×≈FROM ABOVE:

6Wolte3, June 24-26, 1998

DESIGN SOLUTION OF THE NEW PROTOTYPE VERSION (A)

THE FIRST STEP WAS TO REALIZE AN HYBRID MESFET HAVING THE NOISE OF A D-TYPE AND THE DYNAMIC PERFORMANCES OF THE E-TYPE.

THE EASIER WAY IS TO REALIZE A CASCODE BETWEEN A D-TYPE AND AN E-TYPE D

E

G

S

D

A

THE E-TYPE HA S A VERY LARGE 1/f NOISE AND ALSO POOR TRANSCONDUCTANCE (LARGE WHITE NOISE) WHICH MAY BE REFLECTED AT THE INPUT OF THE STRUCTURE.

THINKS ARE IMPROVED IF AN INTERMEDIATE STAGE IS INSERTED BETWEEN THE INPUT D-TYPE MESFET AND THE E-TYPE MESFET.

THIS CAN BE MADE FOLLOWING TWO POSSIBILITIES:

WITH A M-TYPE MESFET WHICH HAS LARGE TRANSCONDUCTANCE BUT LARGE 1/f NOISE

DG

S

D

A

M

E

WITH A D-TYPE MESFET WHICH HAS LOWER TRANSCONDUCTANCE AND LOW 1/f NOISE;

D

DG

S

D

A E

SOLUTIONS AND HAS BEEN IMPLEMENTED.

RESULTS WILL BE PRESENTED ONLY FOR VERSION .

7Wolte3, June 24-26, 1998

DESIGN SOLUTION OF THE NEW PROTOTYPE VERSION (B)

M

D

E

SG

C

DA

A SECOND IDENTICAL CHANNEL IS LOCATED HERE

SECOND STAGE

D

S

G

ED

A

D 3 × 50000 μm2

E 3 × 500 μm2

M 3 × 5000 μm2

D 3 × 25000 μm2

E 3 × 500 μm2

2.5mm

2.5m

m

8Wolte3, June 24-26, 1998

EXPERIMENTAL RESULTS: DC CHARACTERISTICS (A)

E

250M

DW=50000

15K

VDDS

GATE

VIDS

VOFFSETDRAIN

GROUND

= SEMICONDUCTOR ANALYZER (HP4142B) CONNECTIONS

0

0.5

1

1.5

2

0 2 4 6 8 10 12Vds [Volt]

Ids

[mA]

T=77KΔVgs(STEP)=10mVVgs=- 0.65V

0

0.005

0.01

0.015

0.02

0.025

0 2 4 6 8 10 12Vds [Volt]

Ids

[Am

p]

-1.1V<Vgs<-.8V 20 mV step T=300K

9Wolte3, June 24-26, 1998

EXPERIMENTAL RESULTS: DC CHARACTERISTICS (B)

0.5

0.7

0.9

1.1

1.3

1.5

2 4 6 8 10 12Vds [Volt]

Ids

[mA]

T=77KΔVgs(STEP)=10mV TRANSCONDUCTANCE ≈ 30mA/V @ 1mA BIAS CURRENT FOR THE D-TYPE INPUT MESEFT;

OUTPUT IMPEDANCE ≈ 1MegΩ

μ = gm× RDS ≈ 30000 !

0.E+001.E-032.E-033.E-034.E-035.E-036.E-037.E-038.E-03

0 2 4 6 8Vds [Volt]

Ids

[Am

p]

-.9V<Vgs<-.5V 20 mV step

T=4.2K EVEN AT 4.2K THE BREAKDOWN OF THE SUPERFET IS STILL OF CONSIDERABLE VALUE.

10Wolte3, June 24-26, 1998

EXPERIMENTAL RESULTS: DC CHARACTERISTICS (C)

WHILE THE OUTPUT IMPEDANCE AND BREAKDOWN DEPEND MAINLY ON THE DOUBLE CASCODE ACTION, THE TRANSCONDUCTANCE OF THE SUPERFET DEPENDS ON THE OPERATING CURRENT OF THE INPUT MESFET AND CAN BE MODULATED BY ADJUSTING ITS BIASING CURRENT.

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

-1 -0.8 -0.6 -0.4

Vgs [Volt]

Ids

[Am

p]

0 mA 3 mA

5 mA

10 mA

T=77K E

250M

DW=50000

15K

VDDS

GATE

VIDS

VOFFSETDRAIN

GROUND

IQ1=0mA3mA5mA10mA

0.0E+005.0E-041.0E-031.5E-032.0E-032.5E-033.0E-03

2 4 6 8Vds [Volt]

Ids

[Am

p]

I = 5 mA

T=77K

ΔVGS=15mV

ΔIDS=1.1mA

TRANSCONDUCTANCE REACH A VALUE OF THE ORDER OF 100mA/V @ 5mA OF DRAIN CURRENT FOR THE INPUT D-TYPE MESFET TRANSISTOR.

11Wolte3, June 24-26, 1998

EXPERIMENTAL RESULTS: DC CHARACTERISTICS (D)

1.E-121.E-111.E-101.E-091.E-081.E-071.E-06

-1 -0.8 -0.6 -0.4Vgs [Volt]

Ids

[Am

p]

- 0.5 V- 1 V

- 1.5 V

- 2 VT=77K

THE INPUT GATE CURRENT HAS BEEN ALSO STUDIED THANKS TO THE POSSIBILITY TO CHANGE THE DRAIN VOLTAGE OF THE INPUT MESFET.

E

250M

DW =50000

15K

V D D S

G ATE

V ID S

V O FFSETD R A IN

G R O U N D

+

-

VGS OF THE M-TYPE MESFET IS SLIGHTLY LARGER THAN 2V.

IF PARALLEL NOISE HAS TO BE MINIMIZED, THE RIGHT REGION OF OPERATION IS BETWEEN 0.5V AND 1V FOR THE VDSOF THE INPUT D-TYPE MESFET.

THIS WAY THE INPUT GATE CURRENT IS LESS THAN 10nA.

Sup

SupFINAL VERSION

VDDS=-2V-1.5V-1V-0.5V

12Wolte3, June 24-26, 1998

EXPERIMENTAL RESULTS: DYNAMIC CHARACTERISTICS (E)

Sup

E

EBOUT

VCC

E

}D1,.., D5

VEE

500

D

Rf

CfINPUT

= CURRENT GENERATOR

=OUTPUT BUFFER

= FEEDBACK NETWORK

Sup -A

Cf

Rf

13Wolte3, June 24-26, 1998

EXPERIMENTAL RESULTS: DYNAMIC CHARACTERISTICS (F)

T=300KVs=9.6VIsup=10mA

T=77KVs=10VIsup=10mA

T=77KVs=0.35VIsup=10mA

T=4.2KVs=10VIsup=10mA

Sup -A

Cf = 6.8p

Rf = 100K

100

1004.7p

150pSTEP

14Wolte3, June 24-26, 1998

EXPERIMENTAL RESULTS: NOISE PERFORMANCES (A)

f

dCCgain Pre

21

≈

2ne

-A

Cf = 6.8p

Rf = 10Meg

100

1004.7p

Cd3600p GAIN = 50

50

HP4195A: SPECTRUM ANALYZER

Sup

THE MEASUREMENT SYSTEM WAS PUT INSIDE A FARADAY CAGE.

15Wolte3, June 24-26, 1998

EXPERIMENTAL RESULTS: NOISE PERFORMANCES (A)

SO FAR THE SERIES NOISE AS BEEN MEASURED AT 77K.

0.1

1

10

0.01 0.1 1 10f [MegHz]

nV/ √

Hz

Vds=1VId=16mASimulated Noise

T=77K 2f

2n

V A

Hz0.21nV/ e14104.9 −×=

=

0.1

1

10

0.01 0.1 1 10f [MegHz]

nV/ √

Hz Vds=500mVId=16mASimulated Noise

T=77K

2f

2n

V A

Hz0.21nV/ e14103.10 −×=

=

INTERPOLATING FORMULA: HznV/ f

A e e f2n

2T +=

THE NOISE PARAMETERS USED IN THE INTERPOLATING FORMULA ARE NOT AMATHEMATICAL FIT, BUT ARE EXTRACTED FROM ANOTHER MEASUREMENT…….

16Wolte3, June 24-26, 1998

EXPERIMENTAL RESULTS: NOISE PERFORMANCES (B)

ROHDE SCHWARZ URE3: RMS VOLTMETER

RC2-CR2

τ

-A

Cf

Rf = 10Meg

100

1004.7p

Cd

GAIN = 50

50Sup

2ov

( )( )2f

2nf2

n

2

f

fid2o C

i f

A e C

CCC vω

+⎥⎦⎤

⎢⎣⎡ +⎥

⎦

⎤⎢⎣

⎡ ++=

OUTPUT VOLTAGE: TRANSLATED TO CHARGE:

( ) 2ω

2nf2

n2

fid2o

i f

A e CCC Q +⎥⎦⎤

⎢⎣⎡ +++=

FINALLY AT THE VOLTMETER OUTPUT WE GET THE INTEGRATED CHARGE, WHICH, AFTER CALIBRATIONGIVES:

2ne

2ni

( ) 2nf

2n2

fid2

RMS i A e CCC ENCQ γτβατ

+⎥⎥⎦

⎤

⎢⎢⎣

⎡+++==2

17Wolte3, June 24-26, 1998

( ) 2nf

2n2

fid2 i A e CCC ENC γτβα

τ+

⎥⎥⎦

⎤

⎢⎢⎣

⎡+++=

EXPERIMENTAL RESULTS: NOISE PERFORMANCES (C)

y = 5.3616x + 2677.1R2 = 0.9655

y = 5.1838x + 1654.5R2 = 0.9906

y = 6.5634x + 2619R2 = 0.9782

y = 7.8021x + 2830.9R2 = 0.9997

-2000

3000

8000

13000

18000

23000

-1000 0 1000 2000 3000

Cd (pF)

ENC

(el)

ENC (20ns)ENC (50ns)ENC (100ns)ENC (200ns)Lineare (ENC (100ns))Lineare (ENC (200ns))Lineare (ENC (50ns))Lineare (ENC (20ns))

Vds=0.5VIds=16mA

y = 1690.6x + 19.478R2 = 0.9714

0

10

20

3040

50

60

70

0 0.01 0.02 0.03

1/tau (nsec)

Slop

e^2

Sl̂ 2Linear (Sl̂ 2)

Vds=0.5VIds=16mA

BY VARYING THE INPUT CAPACITANCE Cd A STRAIGHT LINE PROPORTIONAL TO ONLY THE SERIES NOISE IS OBTAINED.

f

2n2 A e SL βατ

+=

THE TERMS OF THE LINEAR FIT GIVE THE VALUE OF THE SERIES NOISE AND THE 1/f NOISE TO BE USED IN THE SPECTRUM.

FOR IDS=16mA AND VDS=0.5V WE GET:

2f

2n

V A

Hz0.21nV/ e14103.10 −×=

=

18Wolte3, June 24-26, 1998

EXPERIMENTAL RESULTS: NOISE PERFORMANCES (D)

y = 5.6472x + 1574.9R2 = 0.9982

y = 4.7762x + 1570.6R2 = 0.9973

y = 6.5634x + 2619R2 = 0.9782

y = 7.8021x + 2830.9R2 = 0.9997

-1000

4000

9000

14000

19000

24000

-1000 0 1000 2000 3000

Cd (pF)

ENC

(el)

ENC (20ns)ENC (50ns)ENC (100ns)ENC (200ns)Lineare (ENC (100ns))Lineare (ENC (200ns))Lineare (ENC (50ns))Lineare (ENC (20ns))

Vds=1VId=16mA

y = 1908.4x + 17.866R2 = 0.9659

01020304050607080

0 0.01 0.02 0.03

1/tau (nsec)

Slop

e^2

SL^2Linear (SL^2)

Vds=1VId=16mA

CONSIDERATION: ( ) A e CCC ENC f

2n

fid βατ

+++≈ FOR LARGE Cd VALUES.

BUT THE PREAMPLIFIER ADDS A POLE TO THE OVERALL TRANSFER FUNCTION GIVEN BY:

fidf

Tam CCCCp

++≈ ω

SOLUTION:ENC IS PROPORTIONAL TO Cd + Cf, WHILE THE BANDWIDTH OF THE PREAMPLIFIER IS PROPORTIONAL TO Cf OVER Cd RATIO.

CHANGING BOTH Cf AND Cd WITH THE SAME RATIO AVOIDS THE PREAMPLIFIER ERROR IN THE TRANSFER FUNCTION

*

* NIM Vol. A362, p.466 (1995)

2f

2n

V A

Hz0.21nV/ e14104.9 −×=

=

19Wolte3, June 24-26, 1998

SUMMARY

A LOW NOISE GaAs MESFET, THE SUPERFET, ABLE TO WORK AT CRYOGENIC TEMPERATURES AND ABLE TO SUSTAIN LARGE VOLTAGE SWING HAS BEEN DESIGNED AND REALIZED.

THE MESFET AREA IS LG×W= 3 ×50000, THE SERIES WHITE NOISE IS ABOUT 0.21nV/√Hz, WHILE THE 1/f COMPONENT HAS A COEFFICIENT OF ABOUT 10-13 V2.

THANK TO THE USE OF A LOW DOPED MESFET IN CASCODE WITH THE INPUT MESFET A NEW EQUIVALENT DEVICE IS REALIZED, CAPABLE TO HAVE A VOLTAGE SWING AS LARGE AS 12V AT 77K.

A FIRST MONOLITHIC TEST STRUCTURE HAS BEEN IMPLEMENTED ON A MONOLITHIC CHIP, TO TEST THE DEVICE.

THE DOMINANT POLE AMPLIFIER REALIZED HAS PROVED THE DYNAMIC POTENTIALITY OF THE SUPERFET : SIGNAL SWING OF 10V HAS BEEN MEASURED.

NOISE CHARACTERISTIC HAS BEEN ALSO VERIFIED BY MEASURING THE NOISE OF THE SUPERFET WITH THE DOMINANT POLE AMPLIFIER FEEDBACK AS A CHARGE SENSITIVE PREAMPLIFIER: INPUT NOISE IS AFFECTED IN A NEGLIGIBLE WAY BY THE SECOND STAGE