LOW NOISE SILICON JFETs WORKING AT LOW TEMPERATURES …

1WOLTE 4, 20-23 JUNE 2000, NORTWIJK, THE NETHERLANDS

LOW NOISE SILICON JFETs WORKING AT LOW TEMPERATURES FOR

BOLOMETRIC DETECTOR READOUT

A.Alessandrello, C.Brofferio, O.Cremonesi, A.Fascilla, A.Giuliani, A.Nucciotti, M.Pavan, M.Perego, G.Pessina,

E.Previtali

Dipartimento di Fisica dell’Università di Milano-Bicocca andIstituto Nazionale di Fisica Nucleare,Via Celoria 16, 20133 Milano, Italy

Mark W. Lund

MOXTEK Inc., 452 West 1260 North, Orem UT 84057, USAE-MAIL: [email protected]

WEB: http://crio.mi.infn.it /wig


THE μ-BOLOMETRIC DETECTORS

A PARTICLE OF ENERGY U HITS THE ABSORBING CRYSTAL

vBIASRL

(AN ABSORBINGCRYSTAL IS LOCATED AT VERY LOW TEMPERATURE, <100 mK)

VO

TCU = TΔ

THE TEMPERATURE CHANGE IS INVERSELY PROPORTIONAL TO THE CRYSTAL HEAT CAPACITY

A THERMISTOR CONVERTS THE TEMPERATURE CHANGE IN A VOLTAGE

PRINCIPLE OF OPERATION

HERE WE NEEDA CRYOGENICREADOUT


THE DETAILS OF THE BOLOMETER

DETECTOR CROSS SECTION

THE FINAL ASPECT OF A SINGLE CHANNEL, ABOUT 1x1 mm2.

THE ABSORBING CRYSTAL MATERIAL IS SELECTED TO SATISFY THE EXPERIMENTAL NEEDING.


EXPERIMENTAL RESULTS

WE HAVE BEEN THE FIRST GROUP TO PUSH THE RESOLUTION OF A μ-BOLOMETER DOWN TO 5 eVFWHM. THE DETECTOR WAS COMPOSED BY A NUCLEAR TRANSMUTATING DOPED Ge THERMISTOR GLUED ON A CRYSTAL OF TIN ACTING AS ABSORBER.

(THERMISTOR DIMENSIONS: 300X100X20 μm3

TIN ABSORBER DIMENSION: 250X250X25 μm3)

OUR BEST RESULT OBTAINED WITH ION IMPLANTED Si:P THERMISTOR ON A TIN ABSORBER. FOR THIS CASE THE THERMISTOR VOLUME IS ABOUT TWICE THE NTD ONE.


THE EXPERIMENT WITH μ-BOLOMETERS: THEORY AND APPLICATION

WE ARE STARTING NOW AN EXPERIMENT WITH 10 DETECTORS EACH ONE COMPOSED BY A Si:P THERMISTOR GLUED ON A AgReO4 (SILVER PERRHENATE) FOR THE STUDY OF THE NEUTRINO REST MASS, FOLLOWING THE REACTION:

e-187187 eOsRe ν++→ WITH AN ENDPOINT ENERGY OF 2460 eV.

CALIBRATION SOURCE ADDED

NATURALβ SPECTRUM

KURIE PLOT:

0m HENERGY WIT vs HIT OF N.ENERGY vs HIT OF N.

=ν


THE EXPERIMENT WITH μ-BOLOMETERS: PRELIMINARY RESULTS AND SETUP

THE 10 CH. COLD ELECTRONIC READOUT. THE DETECTOR ARRAY COMPOSED OFTHE 10 μ-BOLOMETERS

DET MASS #mis V_tot R_bol T_bol dV_6 dv_rms dE_0 tau_r dE_Al** ug mV MOhm mK uV uV eV ms eV

s5h4m 323 R0346 s5h4p 259 R0351 100 13.1 52.1 151 0.56 17.1 0.92 22.7 s5h4q 269 R0354 100 12.3 53.0 129 0.79 19.4 0.99 26.2 s5h4s 286 R0356 100 13.3 52.0 143 0.52 16.7 1.10 22.2 s5h4t 284 R0358 100 15.5 50.0 143 0.86 17.0 1.0 24.9

s5h4u 312 R0360 100 12.3 53.0 66.5 0.63 40.5 0.90 50.1+/-2.3

s5h4v 323 R0361 100 14.1 51.2 137 0.80 20.7 1.16 23.9

s5h4z 376 R0363 100 10.9 54.7 122 0.58 20.8 1.6 27.0+/-1.5

s5g4a 272 R0365 100 9.7 56.4 102 0.55 18.4 1.3 22.5+/-0.4

s5g4b 240 R0367 100 8.4 58.5 102 0.57 21.3 0.93 21.0+/-1.5


THE VERY FRONT-END READOUT AND SPECIFICATIONS

vBIAS

RL

VB

T ≤ 60 mK T≈ 115 K ROOM TEMP.

VDRAIN

RS

VSOURCE

TO THE SECOND STAGE

0.5 TO 1 mW MAX

• POWER DISSIPATION MUST BE MINIMAL. IN OUR EXPERIMENT IT CAN RANGES BETWEEN 0.5 AND 1 mW/CH;

• ALTHOUGH NOT VERY FAST, A FEW kHz AT MOST, THE THERMISTOR DYNAMIC IMPEDANCE IS LARGE. CONSEQUENTLY THE INPUT CAPACITANCE OF THE COLD JFET SHOULD BE SMALL;

• TRANSCONDUCTANCE MUST NOT BE TOO SMALL OTHERWISE THERE CAN BE A LOSS IN THE VOLTAGE GAIN;

• LOW FREQUENCY (AND WHITE) NOISE MUST BE VERY SMALL.


SILICON JFET FOR CRYOGENIC OPERATION

JFETTYPE

TEMP.(K)

Cgd + Cgs(pF)

Cgd(pF)

Cgs(pF)

BIASCONDITIO

NS

MX11CA 127 2,23 1,04 1,19 Vds=1,00VIs=1mA

MX11CD 128 6,51 3,07 3,44 Vds=1,00VIs=1mA

126 3,75 2,46 1,29

Vds=1,00VIs=1mAgate tosubstrate =0,5VMX16RC

122 42,1 19,2 22,9Vds=1,00VIs=1mAgate shorted

MX17OLD 129 21,8 11,8 10,0 Vds=1,00VIs=1mA

MX17 130 20,8 12,3 8,5 Vds=1,00VIs=1mA

SO FAR WE MADE A SYSTEMATIC SEARCH OF JFET TRANSISTORS CAPABLE TO SHOW LOW NOISE AT SMALL CURRENT AND AT CRYOGENIC TEMPERATURES.

BETTER RESULTS HAS BEEN OBTAINED WITH THE SILICON JFET PROCESS BY MOXTEK.

TRANSISTORS BY MOXTEK ARE CHARACTERIZED BY AN AREA, OR INPUT CAPACITANCE, WHICH FULFILL THE RANGE NEEDED FOR OUR APPLICATION.

TO THIS PURPOSE WE HAVE DEVELOPED A VERY SIMPLE AND ACCURATE METHOD TO MEASURE THE INPUT CAPACITANCE OF TRANSISTORS AT ANY TEMPERATURE.

ONE PARAMETER OF SELECTION HAS BEEN THE INPUT CAPACITANCE.

THIS DEVICES ARE ESPECIALLY DESIGNED TO OPERATE AT CRYOGENIC TEMPERATURES.

MOXTEK PROCESS CHARACTERISTICS:

CHANNEL RESISTIVITY: 0.45 W/ ;CHANNEL THICKNESS: 1.5 μm;GATE LENGTH: 2 μm;DOPING CONC.: 1016a/cm3


STATIC CHARACTERISTIC OF THE MOXTEK JFET AND MODELING

SO FAR WE STARTED AN ACCURATE CHARACTERIZATION OF THE MOXTEK PROCESS, STARTING FROM THE MODELING.

THE FIRST OBSERVATION WAS THAT THE CLASSICAL MODELS ARE NOT ABLE TO ACCOUNT FOR THESE TRANSISTORS (AND IN GENERAL) AT ANY TEMPERATURE IF THEY ARE OPERATED AT A CURRENT MUCH SMALLER THAN THE MAXIMUM HANDLED CURRENT IDSS.

THE GRADUAL CHANNEL APPROXIMATION AND THE HYPERBOLIC FUNCTION ARE NOT ADEQUATE MODELS FOR THESE DEVICES.

MX11CD: HYPERBOLIC FUNCTION

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2

0 0.5 1 1.5 2

VDS (V)

IDS (mA)

MEASURED DATAHYPERBOLIC

T= 130 K

MX11CD: GRADUAL CHANNEL APPROXIMATION

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0 0.5 1 1.5 2

VDS (V)

IDS (mA)

MEASURED DATAGRA. CH. APPR.

T= 130 K

V GS= -

3.428

V

ΔVGS=20 mV


LIMITS OF THE CLASSICAL MODELS

( )

( )[ ] ( )⎪⎪⎪

⎩

⎪⎪⎪

⎨

⎧

−≤+−−

−≥+⎟⎟⎠

⎞⎜⎜⎝

⎛−

=

V V V V1 VVV2VVI

V V V V1VV1I

I

TOGSDSDSDSTOGS2TO

DSDSS

TOGSDSDS

2

TOGS

DSS

D

λ

λGRADUAL CHANNEL APPROXIMATION

( )DSTOGS

DS2

TOGS

DSSDS V1 VV

V tanhVV1II λα +⎟⎟

⎠

⎞⎜⎜⎝

⎛−⎟⎟

⎠

⎞⎜⎜⎝

⎛−=

HYPERBOLIC FUNCTION

WHY THE TWO MODELS DO NOT SATISFY THE CHARACTERISTICS?

AT CURRENTS MUCH SMALLER THAN IDSS THE DRAIN CURRENT IS NOT A QUADRATIC FUNCTION OF VGS;

THE TRANSITION BETWEEN LINEAR AND SATURATION REGION HAS A SHAPE WHICH DEPENDS ON THE CURRENT. IN ADDITION AT VERY SMALL CURRENTS THERE IS A CHANGE IN THE CONCAVITY.

THE OUTPUT CONDUCTANCE HAS A SLOPE WHICH IS NOT CONSTANT, BUT

DEPEND ON THE GATE VOLTAGE.


HOW TO EXTRAPOLATE THE PINCH-OFF VOLTAGE VTO?

IN THE 2 GRAPHS IT IS EVIDENT THE CHANGE OF THE CONCAVITY AT THE POINTS WHERE THE LINEAR REGION MERGES WITH THE SATURATION REGION.

THE EXTRACTION OF THE PINCH-OFF VOLTAGE HAS BEEN MADE BY CONSIDERING THE OPERATION IN THE SO CALLED SUBTHRESHOLD REGION.THE GATE TO SOURCE VOLTAGE VGS IS FREE TO BE SMALLER THAN VTO (BY NEGATIVE VALUES), BY CONSIDERING AN EXPONENTIAL DEPENDENCE AT VERY SMALL CURRENTS.

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0 0.5 1 1.5 2

VDS (V)

IDS (mA) MX11BDT= 130 KVTO=-3.71 VIDSS=274 mA @ VDS=1 VV GS

= -3.428 V

ΔVGS= 20 mV

0

1

2

3

4

5

6

7

8

9

10

0 1 2 3 4 5 6 7 8 9 10

VDS (V)

IDS (μA)

MX11BDT=130 KVTO= -3.71 VIDSS= 274 mA @ VDS=1 V

V GS= -3.936 V

ΔVGS= 20 mV


SUBTHRESHOLD OPERATION

BEYOND PINCH-OFF IT REMAINS A VERY THIN CHANNEL WITH A DEPTH OF THE ORDER OF THE DEBYE LENGTH.

ELECTRONS CAN TRAVEL FROM THE SOURCE TO THE DRAIN BY DIFFUSION AND THE CURRENT DEPENDS EXPONENTIALLY ON THE DIFFERENCE IN THE CONCENTRATION AT THE SOURCE AND DRAIN, JUST AS IN A BIPOLAR TRANSISTOR.

AS A CONSEQUENCE THE DRAIN CURRENT DEPENDS EXPONENTIALLY ON BOTH GATE AND DRAIN VOLTAGE IN SUBTHRESHOLD.

qTK V e1 e eI B

TVV-

VV-

VV-

DS T

DS

T

GS

T

TO

=⎥⎥⎥

⎦

⎤

⎢⎢⎢

⎣

⎡

−÷⎟⎟⎠

⎞⎜⎜⎝

⎛⎟⎟⎠

⎞⎜⎜⎝

⎛⎟⎟⎠

⎞⎜⎜⎝

⎛


( ){ } ( ){ })V,D(V V1 V)G(V I DSGSDS2

GSGSDS λβ +−= TOV

MODEL FORMULATION

OUR MODEL IS SEMI-EMPIRICAL. IT IS DEFINED TO REDUCE TO THE CLASSICAL QUADRATIC MODEL AT LARGE CURRENT:

( ){ } ( ){ }DS2

GSDS V1V I λβ +−= TOV

BUT ALSO TO ACCOUNT FOR THE NON-QUADRATIC BEHAVIOR AND THE SUBTHRESHOLD OPERATION AT SMALL CURRENTS.

TO THIS AIM WE ADD TWO ADDITIONAL TERMS TO THE CLASSICAL MODEL DEFINED TO SATISFY:

( ){ } ( ){ }DS2

GSDS V1V I λβ +−= TOV

e1 e eI T

DS

T

GS

T

TO

VV

-V

V-

VV

-

DS

⎥⎥⎥⎥

⎦

⎤

⎢⎢⎢⎢

⎣

⎡

−÷⎟⎟⎠

⎞⎜⎜⎝

⎛⎟⎟⎠

⎞⎜⎜⎝

⎛⎟⎟⎠

⎞⎜⎜⎝

⎛

I DS→

I DSS

IDS →0ADDED TERMS


GATE VOLTAGE DEPENDENCE

( ){ } ( ){ })V,D(V V1V)G(V I DSGSDS2


( ) ( ) ( )( )

( ) ( )( )TOGS

TOGS

VVtTOGS

VVtTO

TOeVV

eVV

−

−

+−

−=−

2

2GS2

GSGSV

V)G(Vγ

TO ACCOUNT FOR THE NON-QUADRATIC BEHAVIOR AND SUBTHRESHOLD OPERATION THE TERM G(VGS) WHICH HELP CONVERGENCE OF THE MODEL WAS ASSUMED AS:

( )2GSV TOV−

( )( )

γ

TOGS VVte −

V GS→

0

VGS →

vTO

PARAMETERS: t, γ AND VTO



( ){ } ( ){ })V,D(V V1V)G(V I DSGSDS2


( ) ( )( )( ) ( )DSGS

DSGSDSVmDSDSGS VV

VVVeVVV DS

)(1)(1

1 1),(D TOGS V/V1α

λλ

++

−=+ −−

THE DEPENDENCE OF THE DRAIN CURRENT WITH VDS AND VGS IS MORE COMPLICATED. IT MUST ACCOUNT FOR:

• CONCAVITY CHANGE WITH VGS;

• SLOPE DEPENDENCE ON VGS AT LARGE VDS;

• SUBTHRESHOLD OPERATION.

SUBTHRESHOLDOPERATION

THE CONCAVITY AT SMALL CURRENTS ASKS FOR AT LEAST A QUADRATIC VDSDEPENDENCE AT SMALL VDS.



∑ ⎟⎟⎠

⎞⎜⎜⎝

⎛−=

=

3

0 TO

GS 1VV

)(K

K

KGSV αα

( ) ( )( )( ) ( )DSGS

DSGSDSVmDSDSGS VV

VVVeVVV DS

)(1)(1

1 1),(D TOGS V/V1α

λλ

++

−=+ −−

y = 93125x3 - 15587x2 + 833,02x - 9,4501R2 = 0,9777

y = 17438x3 - 2679.9x2 + 117.96x - 0.7663R2 = 0.973

00.10.20.30.40.50.60.70.80.9

1

0 0.02 0.04 0.06 0.08 0.1

1-VGS/VTO

λ

0

1

2

3

4

5

6α

BY LETTING THE PARAMETERS THAT ACCOUNT FOR THE CONCAVITY AND SLOPE OF THE CURVE TO BE FREE WITH RESPECT TO VGS WE OBTAINED AN INTERESTING RESULT:

∑ ⎟⎟⎠

⎞⎜⎜⎝

⎛−=

=

3

0 TO

GS 1VV

)(K

K

KGSV λλ

PARAMETERS:m, αi, λi i = 0,..,3


APPLICATION OF THE MODEL TO THE MX11CD DEVICE

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0 0.5 1 1.5 2

VDS (V)

IDS (mA) MX11BDT= 130 KVTO=-3.71 VIDSS=274 mA @ VDS=1 V

NO DIFFERENCE!

AT ANY TEMP.

IDSS HAS ITS MAXIMUM AROUND 150 K.VTO DECREASE CLOSE TO 2 mV/OC, AS EXPECTED AT RELATIVELY HIGH DOPING CONCENTRATION:

y = 7E-05x3 - 0.049x2 + 9.7567x - 333.7R2 = 0.9838

y = -0.0018x - 3.4828R2 = 0.9993

-4.05-4

-3.95-3.9

-3.85-3.8

-3.75-3.7

-3.65-3.6

-3.55

0 50 100 150 200 250 300 350

T (K)

VTO (V)

0

50

100

150

200

250

300

IDSS (mA)

MX11BD

CIN= 6.51 pF AT COLD

0

0,2

0,4

0,6

0,8

1

1,2

1,4

1,6

0 0,5 1 1,5 2

VDS (V)

IDS (mA)

MEASURED DATAFITTED DATA

MX11BDT= 300 KVTO=-4.01 VIDSS=126 mA @ VDS=1 V

VGS= -3.62 V

ΔVGS= 20 mV

0

0,2

0,4

0,6

0,8

1

1,2

1,4

0 0,5 1 1,5 2

VDS (V)

IDS (mA)


MX11BDT= 277 KVTO=-3.97 VIDSS=147 mA @ VDS=1 V

VGS= -3.62 V

ΔVGS= 20 mV

0

0,2

0,4

0,6

0,8

1

1,2

1,4

1,6

0 0,5 1 1,5 2

VDS (V)

IDS (mA) MEASURED DATA FITTED DATAMX11BDT= 227 KVTO=-3.88 VIDSS=197 mA @ VDS=1 V

VGS= -3.56 V

ΔVGS= 20 mV

316d

i

2d

i

10N FOR dT

ddT

dV

2

aqNV

cmaTO

sTO

≥Φ

≈

−Φ=ε


APPLICATION OF THE MODEL TO THE MX17 DEVICE

y = 0.0001x3 - 0.0885x2 + 17.32x - 773.96R2 = 0.9725

y = -0.0014x - 3.7263R2 = 0.9285

-4.2

-4.15

-4.1

-4.05

-4

-3.95

-3.9

-3.85

-3.8

0 50 100 150 200 250 300 350

T (K)

VTO (V)

0

50

100

150

200

250

300

350

IDSS (mA)

CIN= 20 pF AT COLD

0

0,2

0,4

0,6

0,8

1

1,2

1,4

1,6

1,8

0 0,5 1 1,5 2

VDS (V)

IDS (mA)MEASURED DATAFITTED DATA

T= 82 K

VGS= -3.22 V

ΔVGS= 20 mV

VTO= -3.88 V0

0,2

0,4

0,6

0,8

1

1,2

1,4

1,6

0 0,5 1 1,5 2

VDS (V)


T= 289 K

VGS= -3.51 V

ΔVGS= 20mV

VTO= -4.14 V

0

0,2

0,4

0,6

0,8

1

1,2

1,4

1,6

1,8

0 0,5 1 1,5 2

VDS (V)

IDS (mA) MEASURED DATAFITTED DATAT= 231 K

VGS= -3.50 V

ΔVGS= 20 mV

VTO= -4.05 V0

0,20,40,60,8

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0 0,5 1 1,5 2

VDS (V)


T= 177 K

VGS= -3.44 V

ΔVGS= 20 mV

VTO= -3.92 V

00,0010,0020,0030,0040,0050,0060,0070,0080,009

0 2 4 6 8

VDS (V)

IDS (mA) MEASURED DATAFITTED DATA

T= 177 K

VGS= -3.82 V

ΔVGS= 10 mV

VTO= -3.96 V


APPLICATION OF THE MODEL TO THE MX16 DEVICE

CIN= 42 pF AT COLD

y = 2E-05x3 - 0.0151x2 + 3.106x - 110.77R2 = 0.8087

y = 2E-05x3 - 0.0151x2 + 3.106x - 110.77R2 = 0.8087

y = -0.0022x - 1.3133R2 = 0.9847

-2.5

-2

-1.5

-1

-0.5

0

0 50 100 150 200 250 300 350

T (K)

VTO (V)

0102030405060708090100

IDSS (mA)

0

0,2

0,4

0,6

0,8

1

1,2

1,4

1,6

0 0,5 1 1,5 2

VDS (V)

IDS (mA)FITTED DATAId interpolata

T= 304 K

VGS= -1.46 V

ΔVGS= 20mV

VTO= -2.02 V

0

0,2

0,4

0,6

0,8

1

1,2

1,4

1,6

0 0,5 1 1,5 2

VDS (V)


T= 89 K

VGS= -1.17 V

ΔVGS= 20mV

VTO= -1.51 V

0

0,2

0,4

0,6

0,8

1

1,2

1,4

0 0,5 1 1,5 2

VDS (V)


T= 226 K

VGS= -1.38 V

ΔVGS= 20mV

VTO= -1.80 V

0

0,2

0,4

0,6

0,8

1

1,2

1,4

1,6

0 0,5 1 1,5 2

VDS (V)

IDS (mA) MEASURED DATAFITTED DATA

T= 153 K

VGS= -1.29 V

ΔVGS= 20mV

VTO= -1.63 V

0123456789

10

0 2 4 6 8 10 12

VDS (V)

IDS (mA)


T= 153 K

VGS= -1.55 V

ΔVGS= 20mV

VTO= -1.63 V


NOISE PERFORMANCES OF THE MOXTEK PROCESS

JFET BY MOXTEK HAVE SHOWN EXCELLENT NOISE PERFORMANCE. THEY SEEM TO BE TRANSISTORS IDEAL FOR CRYOGENIC APPLICATION.

VERY FEW COMMENTS ARE NEEDED TO DESCRIBE THE NOISE CHARACTERISTICS.

LET’S START BY THE SETUP USED FOR THE NOISE MEASUREMENT.

COLD

+

-

10

10000 μF

VDD

VCAL

VOUT

VSS

DUT

0.1

1

10

1 10 100 1000 10000 100000

Hz

nV/ √

Hz

SECOND STAGE NOISE FLOOR

THE AMPLIFIER HAS JFET AS INPUT DEVICES

THIS SECOND STAGE HAS BEEN SUBTRACTED IN QUADRATURE.


NOISE OF TH MX16RC THAT HAS 43 pF OF INPUT CAPACITANCE

THE MX16RC IS ACTUALLY A DUAL GATE DEVICE. WHEN THE SECOND, SUBSTRATE, GATE IS NOT CONNECTED WITH THE FIRST, TOP, GATE THE INPUT CAPACITANCE IS ABOUT 3.5 pF. UNFORTUNATELY IF USED AS A UNITY GAIN BUFFER, TRANSCONDUCTANCE REDUCTION FORCE TO SHORT CIRCUIT THE 2 GATES THAT RESULTS IN A LARGER CAPACITANCE.

CONSIDERATIONS:

• THE WHITE NOISE IS QUITE CONSTANT AROUND 110 K;

• LOW FREQUENCY NOISE IS DEPENDENT ON TEMPERATURE

LET’S CONSIDER THE PARAMETER HF , TECHNOLOGY DEPENDENT:

JfF CAH =

HF= 8.2×10-29 J

0.1

1

10

1 10 100 1000 10000 100000

Hz

nV/√Hz131 K 103 K

MX16RCT= 110 KIDS=1 mAVDS=1 VTop and Bottom gates shorted


NOISE OF TH MX17 THAT HAS 21 pF OF INPUT CAPACITANCE

0.1

1

10

1 10 100 1000 10000 100000

Hz

nV/ √

Hz MX17

T= 109 KIDS=1 mAVDS=1 V

126 k

100 K

FOR EACH DEVICE TYPE WE HAVE MEASURED A FEW SAMPLES.

THE AVERAGE RESULT FOR THE MX17 IS THE ONE SHOWN ON THE RIGHT.

IT RESULTS: HF=8×10-28 J.

0.1

1

10

1 10 100 1000 10000 100000

Hz

nV/√Hz

128 K

113 K

MX17GOLDT= 105 KIDS=1 mAVDS=1 V

NEVERTHELESS A PAIR OF SAMPLES SHOWED VERY EXCELLENT NOISE PERFORMANCES.

HF= 4.5×10-29 J


NOISE OF TH MX11BD THAT HAS 6.5 pF OF INPUT CAPACITANCE

2.4×10-29 J< HF< 5×10-29 J0.1

1

10

100

1 10 100 1000 10000 100000

Hz

nV/√HzMX11BDT= 111 KIDS=1 mAVDS=1 V

103 k

121 k

131 K

THE VERY BEST RESULT HAS BEEN OBTAINED WITH THIS DEVICE.

IT HAS SHOWN, PROBABLY, THE LOWER HF EVER SEEN IN A JFET TRANSISTOR.

1


COMPLETE SETUP

FROM THE TIME THE PAPER WAS WRITTEN THING ARE IMPROVED. THE SECOND STAGE NOW HAS A NEGLIGIBLE CONTRIBUTION ON THE OVERALL NOISE PERFORMANCE.

THE COMPLETE SETUP, WHICH IS THE ONE USED WITH THE BOLOMETRIC DETECTORS, IS COMPOSED BY A MX11CD FOLLOWED BY THE NEW SECOND STAGE.

THE INPUT SERIES NOISE OF THE NEW SECOND STAGE AMPLIFIER, HAVING A JFET INPUT PAIR IS SHOWN BELOW:

0.1

1

10

1 10 100 1000 10000 100000

Hz

nV/ √

Hz

second stage input noise only

1/f= 0.89 V2

white= 0.7 nV/√Hz


CONCLUSIONS

THE SILICON JFET PROCESS BY MOXTEK HAS BEEN SELECTED FOR THE REALIZATION OF AN EXPERIMENT WITH BOLOMETRIC DETECTORS.

A NEW STATIC MODEL HAS BEEN DEVELOPED TO ACCOUNT FOR THE BEHAVIOR OF THE DEVICES HAVING LARGE IDSS WHEN OPERATED AT SMALL CURRENTS IDS.

THE MODEL MERGE THE CLASSICAL GRADUAL CHANNEL APPROXIMATION WITH THE SUBTHRESHOLD OPERATION.

THE DEVELOPED MODEL CONSIDER THAT IN SATURATION REGION THERE IS A DEPENDENCE OF THE OUTPUT CONDUCTANCE WITH THE GATE VOLTAGE.

• VERY GOOD NOISE PERFORMANCES HAS BEEN VERIFIED.

• THE OPTIMUM TEMPERATURE OF OPERATION FOR 1/f NOISE WAS FOUND AT ABOUT 110 K.

• VERY SMALL VALUE FOR THE PROCESS NOISE PARAMETER HF=AfCI WERE EXTRACTED FROM THE MEASUREMENTS. BETTER RESULT WAS A FEW TIMES 10-29 J, THE WORST CASE WAS IN ANY CASE ONLY A FEW TIMES 10-28 J!

LOW NOISE SILICON JFETs WORKING AT LOW TEMPERATURES …

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