NASA CASE NO. LAP_lSQ62.=tPRINT FIG.

NOTJCE

The invention disclosed in this document resulted from research in aeronautical

and space activities performed under programs of the National Aeronautics and Space

Administration. The invention is owned by NASA and is, therefore, available for

licensing in accordance with the patent licensing regulations applicable to U.S.

Government-owned inventions (37 CFR 404.1 e1 seq.).

To encourage commercial utilization of NASA-owned inventions, it is NASA

policy to grant licenses to commercial concerns. Although NASA encourages

nonexclusive licensing to promote competition and achieve the widest possible

utilization, NASA will provide the necessary incentive to the licensee to achieve early

practical application of the invention.

Address informational requests for this invention to the Technology

Applications Team, NASA Langley Research Center, Code 200, Hampton, Virginia

23681-0001.

Address applications for license to the Patent Counsel Office, Mail Stop 212,

3 Langley Boulevard, Hampton, Virginia 23681-0001.

Serial No.: 08/416,596

Filed: 04/04/95

(NASA-Case-LAR-15062-1)

MULTI-CHANNEL ELECTRON[CALLY

SCANNEO CRYOGENIC PRESSURE SENSOR

Patent Application (NASA. Langley

Research Center) 27 p

LaRC

N95-27138

Unclas

_f

G3/35 00496?6
NASA Case No. 15062- 1 

MULTI-CHANNEL ELECTRONICALLY SCANNED 

CRYOGENIC PRESSURE SENSOR 

AWARDS ABSTRACT 

There are currently 17 cryogenic wind tunnels in operation worldwide, most operate 

in a temperature range of - 1 90°C to + 70°C. The coldest temperature falls 

approximately 140°C below the lowest mil-spec temperature for the performance 

rating of electronic components. Cryogenics is used to lower flow temperatures to 

achieve high Reynolds numbers by increasing flow density. These low temperatures 

present problems with instrumentation hardware designed to measure pressure when 

subjected to this cold environment. 

A miniature, multi-channel, electronically scanned pressure measuring device uses 

electrostatically bonded silicon dies in a multi-element array. These dies are bonded 

at specific sites on a Pyrex 7740 glass substrate pre-patterned with gold circuit traces. 

In addition, thermal data is multiplexed and recorded on each individual pressure 

measuring diaphragm. 

Novel aspects of the present invention include the ability to function in a cryogenic 

environment without the need of heaters to keep the sensor at constant temperatures. 

The fabrication technique and materials used produce an instrument that will deliver 

repeatable data each time it is thermal cycled without recalibration. In addition, each 

pressure measuring component has its own temperature sensor, thereby eliminating 

thermal offset errors due to changing temperatures. 

Inventors: John J. Chapman Purnell Hopson, Jr. 

Address: Box 102 Glenroy Estates 407 Cheadle Loop Road 

Ware Neck VA 23 178 Seaford. VA 23696 

Nancy M. H. Ihse 

Rt 4 Box 1057 

Employer: NASA LaRC 

Initial Evaluator: Lorelei S. Gibson 

Serial No.: 08/41 6,596 

Filed: APRIL 4,1995 
LAR 15062-1 - 1- PATENT APPLICATION

MULTI-CHANNEL ELECTRONICALLY SCANNED

CRYOGENIC PRESSURE SENSOR

5

]0

Origin of the Invention

The invention described herein was made by employees of the

United States Government and may be manufactured and used by or for

the Government for governmental purposes without the payment of any

royalties thereon or therefor.

Background of the Invention

1. Field of the Invention

]5 This invention relates generally to a pressure sensor and more

particularly to a multi-channel electronically scanned pressure sensor for

cryogenic environments.

2O

25

2. Description of the Related Art

There are currently 17 cryogenic wind tunnels in operation

worldwide, most operate in a temperature range of -190°C to + 70°C.

The coldest temperature falls approximately 140°C below the lowest milspec temperature for the performance rating of electronic components.

In an effort to develop higher lift and lower drag airfoils, aerodynamicists

are striving to study boundary layer behavior at very high Reynolds

numbers. Cryogenics is used to lower flow temperatures to achieve high

Reynolds numbers by increasing flow density. These low temperatures

present problems with instrumentation hardware designed to measure
LAR 15062-1 -2- PATENT APPLICATION

5

10

pressure when subjected to this cold environment.

The prior art uses adhesive bonding of individual silicon pressure

sensing die of silicon or Pyrex. A stress isolation pedestal may also be

incorporated. An adhesive material is required to secure each sensor to

the substrate. Since the adhesive exhibits a large variation in coefficient

of thermal expansion (CTE) with temperature, this results in large

apparent strains being exerted upon the sensors as thermal cycling

occurs. Adhesive materials with critical transition temperatures above

77K will also cause thermally induced offset variations which will cause

non-repeatability of sensor output data in cryogenic applications. This

problem is more accentuated with the use of thinner membrane

thicknesses necessary for accurate measurements in cryogenic wind

tunnels.

]5 Objects of the Invention

2O

25

It is accordingly an object of this invention to provide a device

capable of performing multichannel pressure measurements at cryogenic

temperatures.

It is another object of the present invention to perform the

pressure measurements with increased accuracy, low noise and improved

repeatability at cryogenic temperatures.

Additional objects and advantages of the present invention are

apparent by the drawings and specification which follow.

Summary of the Invention

The present invention overcomes the problem of measuring

pressure in a cryogenic environment. This is accomplished by providing
LAR 15062-1 -3- PATENT APPLICATION

a miniature, multi-channel, electronically scanned pressure measuring

device which uses electrostatically bonded silicon dies in a multi-element

array. These dies are bonded at specific sites on a Pyrex 7740 glass

substrate pre-patterned with gold circuit traces. In addition, thermal data

5 is multiplexed and recorded on each individual pressure measuring

diaphragm.

The electronics package consists of basically two parts: an

amplifier circuit comprised of a monolithic instrumentation amplifier on a

standard printed circuit card, and a gold circuit patterned Pyrex glass

]0 substrate comprised of pressure sensing dies and multiplexing devices.

Pyrex is a trademark of Corning, Inc.

The pressure sensing device utilizes square silicon dies which have

been etched on the back surface to form a very thin silicon diaphragm.

The diaphragm has four highly doped (e.g., boron) piezo-resistive

!5 elements of the same geometry patterned in the diaphragm surface, two

acting in compression and two acting in tension. There is also one

additional bridge element on the die rim, insensitive to pressure, which

provides a temperature measurement of each silicon pressure sensing die

used for temperature compensation. In order for the silicon pressure

20 sensing dice to operate properly below -100°C, it is necessary that the

dopant impurity level be on the order of 1E 2° atoms of boron per cubic

centimeter. This dopant level ensures that the sensors do not suffer

from charge carrier freezeout due to low charge carrier mobility.

The requirement for structural integrity in electronic packaging is

25 met by the use of metallic materials with low coefficients of thermal

expansion such as Kovar. The coefficient of thermal expansion of Pyrex

7740 glass matches that of silicon well enough to tolerate thermal

cycling in properly annealed substrates. The Pyrex substrate is first

metallized with titanium/tungsten for the adhesion layer and then a layer
LAR 15062-1 -4- PATENT APPLICATION

of gold is deposited for good conduction. The circuitry pattern is then

etched to produce low resistance, high quality tracks. The silicon

pressure sensors are bonded to the metallized substrate by field-assisted

thermal bonding. This process takes place at 375°C. It is performed

5 under high vacuum with an applied field strength of 1E6 volts per meter

on the silicon sensors-Pyrex interface. After bonding, the sensor

substrate is then attached to the tubing plate using a thin sheet of

thermosetting polyamide film. The modified polyamide material remains

flexible at -196°C and provides a compliant bond between these two

]0 surfaces. The electrical interconnection of the sensor circuitry to the

substrate is made using a thermo-ultrasonic wedge-ball bonding machine

with substrate heating applied.

A modified, commercially available analog-to-digital converting

data acquisition interface card is used to scan the pressure inputs. Since

]5 the instrumentation module is equipped with its own instrumentation

amplifier and multiplexing circuitry, the interface could be streamlined by

interconnecting the instrumentation amplifier output directly to the

sample and hold input on the PC card with coaxial cable. This improves

the signal to noise ratio since all millivolt level signal leads are contained

20 within the instrument module and are just a few centimeters in length.

Similarly, the multiplexing switches are also within the module. Linking

the address and enable lines from the remote module to the timing

circuitry on the PC card via line drivers and receivers ensures quiet,

reliable operation. The output of the instrumentation amplifier is digitized

2_5 by the A/D card in the PC. Data taken is first stored to RAM, then saved

to diskette and displayed as real-time engineering units on the monitor.

The data rate and sample time interval for a data record is preset by the

scanning software parameters. The menu driven software provides for

access to data files for storage, recall of sensor calibration files and for
LAR 15062-1 -5- PATENT APPLICATION

real time display.

This invention functions in a cryogenic environment without the

need of heaters to keep the sensor at constant temperatures. The

fabrication technique and materials used produce an instrument that will

5 deliver repeatable data each time it is thermal cycled without

recalibration. In addition, each pressure measuring component has its

own temperature sensor, thereby eliminating thermal offset errors due to

changing temperatures.

In addition, the advantage over existing devices is the freedom

|0 from hand mounting of each sensor and freedom from the tedious

application of elastomer or adhesive bonding material to each sensor. The

sensor array is one coupon, just as if it was a VLSl circuit with the

sensors precisely positioned on the substrate without any trace of die

attach adhesive. The application of pressure sensors to make accurate

]5 measurements is greatly enhanced due to this measure. The adhesive

material necessary to attach sensors in prior art is not conducive to

accurate measurements since the elastomeric material expands and

contracts with temperature variations. This undesirable effect applies

mechanical forces to the sensors in such a fashion as to cause drift. The

20 main advantage of this method is in cryogenic applications. The sensors

remain bonded throughout hundreds of thermal cycles and exhibit stable

and repeatable calibrations for years. The accuracy of the sensors is

stable and there is no need for any mechanical calibration valve

apparatus within the measuring instrument.

25 The exact placement of the sensors will facilitate automated or manual

ballbond electrical lead placement. The elastomerically bonded sensors

usually have some randomness to the positioning and also have

elastomeric residue present plus undesirable outgassing fumes from the

curing process can cause corrosive effects on nearby components. The
LAR 15062-1

5

]0

-6- PATENT APPLICATION

main advantage is in the stability, the curing process takes

up to a full year to complete and this effects the measurement accuracy

of the instrument since the elastomeric material induces random drift in

the sensor which cannot be accounted for by any means other than

frequent recalibration which is very costly in the case of wind tunnels.

Another advantage is that the sensing module can operate accurately at

cryogenic temperature and thus does not need auxiliary heaters to

maintain a warm environment during wind tunnel testing. This elimination

of the heating requirement, while maintaining the high accuracy is a great

asset since the model in which the modules reside during the test is not

subject to heating effects from instrumentation within the model. This

has the beneficial effect of allowing the model to remain at the true

freestream temperature of the wind tunnel. Existing technology simply

did not allow this, as a result there was an unwanted disturbance of the

boundary sublayer during cryogenic testing of any model equipped with

auxiliary heaters.

15

Brief Description nf the Drawings

20 FIG.

FIG.

FIG.

FIG.

FIG.

25 FIG.

FIG.

substrate;

la is a top view of a die;

lb is a side view of a die;

2 is a schematic illustration of the resistor arrangement;

3 is a graph of piezoresistance coefficient versus temperature;

4 is a plot of offset hysteresis;

5 is a plot of sensitivity hysteresis;

6 is a cutaway view of a pressure sensor bonded to a

FIG. 7 illustrates the PC interface with the pressure/temperature

calibration system;
LAR 15062-1

5

-7- PATENT APPLICATION

FIG. 8a is a cutaway view of a portion of the fabrication fixture;

FIG. 8b is a side view of the fabrication fixture;

FIG. 8c is a top view of the substrate; and

FIG. 8d is a top view of a portion of the fabrication fixture.

Description of the Preferred Embodiments

The electronics package consists of basically two parts: an

amplifier circuit comprised of a monolithic instrumentation amplifier on a

]0 standard printed circuit card, and a gold circuit patterned Pyrex glass

substrate comprised of pressure sensing dies and multiplexing devices.

Referring to FIGs. la and lb, the electronics device utilizes square

silicon dies 10, approximately 2.54 mm on each side, which have been

etched on the back surface to form a very thin silicon diaphragm 20,

]5 approximately 0.3 mm high. Referring to FIG. 2, the diaphragm 20 has

four highly doped (e.g., boron) piezo-resistive elements 30 of the same

geometry patterned diffused in the diaphragm surface, two acting in

compression and two acting in tension. There is also one additional

bridge element 40 on the die rim, insensitive to pressure, which provides

20 a temperature measurement of each silicon pressure sensing die used for

temperature compensation. As illustrated in FIG. 3, in order for the

silicon pressure sensing dice to operate properly below -100°C, it is

necessary that the dopant impurity level be in the range of lxl01gto

lx10 21 atoms of boron per cubic centimeter. The higher the level of

25 boron, the greater the insensitivity to cold. This dopant level ensures

that the sensors do not suffer from charge carrier freezeout due to low

charge carrier mobility. The piezoresistive pressure sensors are

influenced not only by the thermal offset and sensitivity shifts in the

bridge resistors but also are heavily influenced by mechanical mounting
LAR 15062-1 -8- PATENT APPLICATION

effects between the die and substrate due to temperature dependent

differences in coefficient of thermal expansion between the die and

substrate materials, all of which contribute to the sensor overall thermal

offset drift. Plots of individual sensors, mounted by the preferred method

5 of field assisted bonding to a Pyrex 7740 substrate yield smoothly

varying, repeatable offset and sensitivity curves, as shown in FIGs. 4 and

5, respectively.

The requirement for structural integrity in electronic packaging is

met by the use of metallic materials with low coefficients of thermal

]0 expansion such as Kovar. The coefficient of thermal expansion of Pyrex

7740 glass matches that of silicon well enough to tolerate thermal

cycling in properly annealed substrates. Referring to FIG. 6, the Pyrex

substrate 50 is first metallized with titanium/tungsten for the adhesion

layer 60 and then a 1.5 micrometer layer of gold is deposited 70 for

]5 good conduction. The circuitry pattern is then etched to produce low

resistance, high quality tracks. The silicon pressure sensors 80 are

bonded to the metallized substrate 50 by field-assisted thermal bonding.

This process, otherwise referred to as Mallory bonding by the electronics

industry, takes place at 375°C. It is performed under high vacuum with

20 an applied field strength of lx106 volts per meter on the silicon sensorsPyrex interface. After bonding, the sensor substrate is then attached to

the tubing plate 90 using a thin sheet of thermosetting polyamide film

100. The modified polyamide material remains flexible at -196°C and

provides a compliant bond between these two surfaces. The electrical

25 interconnection of the sensor circuitry to the substrate is made using a

thermo-ultrasonic wedge-ball bonding machine with substrate heating

applied.

A modified, commercially available, high resolution A/D analog to

digital conversion interface card is used to scan the pressure inputs.
LAR 15062-1 -9- PATENT APPLICATION

Referring to FIG. 7, since the instrumentation module is equipped with its

own instrumentation amplifier 66 and multiplexing circuitry 65, the

interface can be streamlined by interconnecting the instrumentation

amplifier output directly to the sample and hold input on the PC card 55

5 with coaxial cable 75. This improves the signal to noise ratio since all

millivolt level signal leads are contained within the instrument module and

are just a few centimeters in length. Similarly, the multiplexing switches

are also within the module. Linking the address and enable lines from

the remote module to the timing circuitry on the PC card via line drivers

!0 and receivers ensures quiet, reliable operation. The output of the

instrumentation amplifier is digitized by the A/D card in the PC. Data

taken is first stored to RAM, then saved to diskette and displayed as realtime engineering units on the monitor. The data rate and sample time

interval for a data record is preset by the scanning software parameters.

!5; The menu driven software provides for access to data files for storage,

recall of sensor calibration files and for real time display.

Referring to FIGs. 1a-b, 2 and 6, four resistive elements 30 on the

die diaphragm 20 are connected in a Wheatstone Bridge configuration by

means of gold wire bonding. A constant D.C. voltage is placed across

20 two legs of the bridge as input voltage, and the other two legs are

voltage outputs. When pressure is applied to the silicon diaphragm a

strain occurs, causing a resistance imbalance in the bridge thereby

causing an output voltage or a change in the existing output voltage on

the output legs of the bridge. This output voltage is applied to a

25 differential multiplexer switch. Referring to FIG. 7, the output of the

multiplexer 65 is tied to the input of an instrumentation amplifier 66. The

fifth element on the die periphery 40 is on part of the silicon die bulk that

supports the thin diaphragm, and the element is patterned in a location

and with a geometry that renders it insensitive to strain, but the element
LAR 15062-1 - 1O- PATENT APPLICATION

changes resistance proportional to temperature. This element is powered

with a constant current and the change in resistance due to change in

temperature produces a change in voltage drop across the element. This

voltage change is connected to a multiplexer switch 65 in the same

5 manner as the pressure sensing elements on the die diaphragm.

Referring to FIG. 7, the pressure measuring module communicates to the

outside world through a personal computer equipped with analog to

digital converters and controlling software. The computer software

produces and delivers binary addresses and phased enable pulses to the

]0 module multiplexer chips which are connected to all the pressure sensing

dies. These computer generated pulses cause the multiplexer chips to

scan the pressure dies and temperature sensors on each die.

Referring again to FIG. 6, fabrication of the sensing portion of this

package involves the electrostatic bonding of highly doped piezoelectric

15 silicon pressure dies 80 to a 7740 Pyrex glass substrate 50. Prior to die

bonding, the glass substrate 50 is metallized, by sputter deposition with

a thin adhesion layer 60, (approximately 1000 Angstroms), of tungsten

with 10% titanium. This adhesion layer 60 is over-coated with

approximately one micrometer of sputtered gold. Both the adhesion layer

20 60 and gold layer 70 are deposited in the same machine without breaking

vacuum. The metallized glass substrate 50 is circuit patterned by

standard photolithography. Referring to FIG. 8b, the metallized and

patterned substrate is then drilled with .025 inch holes 61 at each silicon

die location and thermally annealed in air at 600°C for one hour. This

25 completes the glass substrate preparation.

Referring to FIGs. 8a, 8c and 8d, the silicon dies 150 and the

prepared glass 50 are loaded in a fixture 170 of a dielectric (SiO 2) high

temperature material. The fixture 170 is designed to hold the individual

sensors to form a sensor array. This sensor array is held in position over
LAR 15062-1

5

]0

25

-11- PATENT APPLICATION

the metallized substrate 50 so that each die is precisely positioned over

its .025 inch pressure orifice 160. In addition to positioning, this cast

fixture allows for pressure to be applied to each silicon die 150, to bring

the die into close contact with the glass substrate 50. Contacting

pressure is applied to the silicon die 150 by spring loaded contacts 190

inserted into holes 200 cast in the fixture 170 centered over each

pressure die location. The loaded fixture is placed into a tube furnace

and evacuated to a pressure below 5x10 -6 torr and heated to 375°C.

When the temperature has reached equilibrium, an electrical potential of

800 volts D.C. is applied to the fixture electrodes for five minutes

causing electrostatic bonding of the silicon pressure dies to the glass

substrate 50. The glass substrate with bonded silicon dies are then

mounted to a Kovar pressure tube plate with pressure orifices aligned

over each .025 inch hole in the glass substrate. The fixture was made

by casting soft gel state SiO 2 over a male plug mold having slightly larger

dimensions than the finished sensor array. The SiO2 material was fired in

a kiln just as a ceramic material to make it hard. The SiO2 was chosen

due to its desirable material properties of the fired product, low

temperature coefficient of linear expansion, high dielectric strength,

ability to withstand high temperature, and low outgassing for vacuum

processing during the bonding operation.

Each cavity has the same outline as the individual sensor which is

inserted into the cavity. The depth of the cavity is sufficient to accept

the sensor and a "top hat" piece 220 of silicon with the same outline as

the sensor which is inserted into the fixture before the sensor in order to

distribute the mechanical load induced by the spring loaded pin 190. The

spring loaded pin 190 is used to hold the sensor chip in intimate contact

with the Pyrex substrate 50 during the bonding process. Referring to FIG.

8b, the pin 190 also allows an electrical contact for the bonding

2O

]5
LAR 15062-1 -12- PATENT APPLICATION

potential to be applied to the sensor 250 when the fixture is connected

as shown in FIG. 8d with the end plate (anode) 230 and metallized quartz

bottom cathode 240. For the bonding operation, the top hats 220 are

loaded in the cavities. The sensors 50 are then loaded, membrane side

5 in contact with the top hats 220. The drilled and metallized Pyrex

substrate 50 is put in contact with the sensors 50 and the metallized

quartz cathode 240 is placed against the bottom of the fixture. The

spring loaded pins 190 are inserted from the top of the fixture. The top

plate or anode 230 is then put over the pins 190 and the plates are

]0 secured by stainless bolts 280. The loaded fixture is then placed in a

vacuum oven, pumped down and the oven temperature adjusted to

375°C. An inert atmosphere such as nitrogen, argon or helium could be

used in lieu of evacuation to prevent oxidation. Once thermal equilibrium

is reached, an 800 volt potential is then applied to the fixture, the

]5 bonding takes place in just a few minutes. The oven is then allowed to

cool to room temperature and the fixture is removed, unbolted and

opened up to free the substrate which is ready for mounting on the

tubing plate. A polyamide film adhesive material is used for the

attachment of the sensor array which is comprised of the individual

20 sensors to the tubing plate. This material in thin sheet form has

demonstrated flexibility when dipped in liquid nitrogen since it remains

compliant at cryogenic temperatures. The polyamide sheet is first cut to

the size of the Pyrex substrate and holes are punched to allow gas

conductance of the pressure ports. For the assembly, the polyamide film

25 100 is placed on the tubing plate 90 so the holes line up. The sensor

array Pyrex coupon is then placed upon the polyamide film, with the

holes registered. The tubing plate and positioned array is placed within a

vacuum bag which is then evacuated and placed in an oven at + 125°C.

The polyamide is plastic at high temperatures and flows between the
LAR 15062-1 -13- PATENT APPLICATION

bottom of the Pyrex substrate and the tubing plate. This forms a

compliant layer between the Pyrex coupon and the tubing plate that

withstands the extreme temperatures and remains free from leakage at

cryogenic temperatures. A high temperature polyamide film material may

5 also be used for instruments destined for high temperature applications.

As an alternative, the application of a polyimide in liquid suspension in

solvent is also possible for the purpose of attaching the Pyrex coupon to

the tubing plate. A curing cycle at elevated temperature is required.

After substrate to pressure tubing plate mounting is complete, the

]0 multiplexer chips are mounted on the Pyrex substrate with epoxy.

Multiplexers and silicon dies are gold wire bonded to their prospective

circuit locations. This completes the pressure sensing and scanning half

of the electronics package.

The amplifier is constructed using standard printed circuit board

]5 technology, and utilizes a monolithic instrumentation amplifier as the

active component on the printed circuit card. The amplifier card makes

contact with the pressure sensing substrate through gold plated, spring

loaded contacts soldered to the amplifier card. These spring loaded

contacts are aligned with gold contact pads on the sensing substrate.

20 A system capable of controlling temperatures from -184°C to

+ 220°C and pressures from 0 to 344.74 Kpa was used to calibrate the

sensing module. A thermocouple accurate to within +/- 0.1°C of reading

was used to calibrate the temperature of sensors within the module.

Due to the parallel circuit of the sensor supply bus which

25 necessitates constant voltage excitation, and sensor resistance which

decreases as temperature decreases, the sensors are more sensitive with

decreasing temperature. The hysteresis, however, is less than the

resolution of the encoder.

The measurement of calibration pressures is accurate to within +/-
LAR 15062-1 -14- PATENT APPLICATION

0.01% of full scale (344.74 Kpa). The set point resolution is 3.447 Pa.

Helium is used as the calibration gas. The uncertainty of the temperature

controller is +/- 0.5°C with a temperature deviation of +/- 0.1°C after

stabilization. The repeatability following a temperature reset is +/-

5 0.25°C.

The uncertainty of the analog to digital conversion system used to

scan the pressure module is +/- 0.01% F.S. The resolution of the

analog to digital conversion system is +/- 0.01% F.S. The overall error

of the multichannel pressure sensing system, based on several pressure

]0 and temperature calibrations repeated within 180 days is 0.1% F.S. for -

196°C to + 100°C over the differential pressure range -101.35 Kpa to

+241.32 Kpa.

Many modifications, improvements and substitutions will be

apparent to the skilled artisan without departing from the spirit and scope

]5; of the present invention as described in the specification and defined in

the following claims.

What is claimed is:
LAR 15062-1 PATENT APPLICATION

MULTI-CHANNEL ELECTRONICALLY SCANNED

CRYOGENIC PRESSURE SENSOR

5

]0

Abstract of th_ Di_closure

A miniature, multi-channel, electronically scanned pressure

measuring device uses electrostatically bonded silicon dies in a multielement array. These dies are bonded at specific sites on a glass, prepatterned substrate. Thermal data is multiplexed and recorded on each

individual pressure measuring diaphragm. The device functions in a

cryogenic environment without the need of heaters to keep the sensor at

constant temperatures.

]5
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