ARL-TR-7825 ● SEP 2016

US Army Research Laboratory

A Novel Vacuum Packaging Design Process for 

Microelectromechanical System (MEMS) 

Quad-Mass Gyroscopes

by Rohan Deshmukh, Ryan Knight, and Dr William Nothwang

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ARL-TR-7825 ● SEP 2016

US Army Research Laboratory

A Novel Vacuum Packaging Design Process for 

Microelectromechanical System (MEMS) 

Quad-Mass Gyroscopes

by Rohan Deshmukh

Aerospace Engineering, Georgia Institute of Technology, 

Atlanta, GA

Ryan Knight and Dr William Nothwang

Sensors and Electron Devices Directorate, ARL

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4. TITLE AND SUBTITLE

A Novel Vacuum Packaging Design Process for Microelectromechanical 

System (MEMS) Quad-Mass Gyroscopes

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Rohan Deshmukh, Ryan Knight, and Dr William Nothwang

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US Army Research Laboratory

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2800 Powder Mill Road

Adelphi, MD 20783-1138

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ARL-TR-7825

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14. ABSTRACT

Gyroscopes are an integral component of inertial measurement units. They are important to Army systems as they provide 

Soldiers with information on position, navigation, and timing. The majority of microelectromechanical system (MEMS) 

gyroscopes in production today are vibratory rate gyroscopes, making them resonant systems. Of the various systematic 

performance parameters for resonant systems, the quality factor (Q-factor) is an important measure. Q-factor for resonant 

MEMS such as the quadruple-mass gyroscope (QMG) strongly depends on the pressure at which the system operates. To 

improve upon Q-factor of the existing MEMS gyroscope, a novel submilliTorr vacuum packaging approach was designed. 

The packaging process has been broken down into systematic steps with the goal in each step to reduce internal packaging 

pressure, which was measured using commercial off-the-shelf Pirani gauges. The process was then tested on in-house 

fabricated QMGs, where Q-factor was measured for both short- and long-term stability. The packaging process will be 

valuable for improving MEMS gyroscope performance and pursuing further development.

15. SUBJECT TERMS

gyroscopes, vacuum packaging, hermetic sealing, Pirani gauge, residual gas analyzer

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Ryan Knight

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Contents

List of Figures iv

List of Tables v

1. Introduction/Background 1

1.1 Overview of MEMS Gyroscopes 1

1.1.1 Performance Parameters 3

1.2 Vacuum Packaging Overview 4

1.2.1 General Packaging Procedure 5

1.3 Pirani Gauge Overview 8

2. Experimental Approach 9

2.1 Thermal Fluctuation Experiment 10

2.2 Heating Profile Design 16

2.2.1 Bake Out 18

2.2.2 Ramp-Up 19

2.2.3 Lid Seal 20

2.2.4 Cool/Purge 22

2.3 Residual Gas Analyzer Experiment 23

3. Results 28

4. Conclusions 32

5. Future Work 33

6. References 34

List of Symbols, Abbreviations, and Acronyms 36

Distribution List 37
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List of Figures

Fig. 1 ARL-fabricated QMG............................................................................2

Fig. 2 Size of various devices following the technology trend ........................2

Fig. 3 Theoretical model of a single z-axis vibratory gyroscope .....................3

Fig. 4 MEMS gyroscope performance vs. cost tradeoff ..................................5

Fig. 5 Overall MEMS vacuum packaging procedure.......................................5

Fig. 6 Example die attachment schematic........................................................6

Fig. 7 Example wirebond between MEMS die and package ...........................7

Fig. 8 Post-packaging vacuum lid seal.............................................................7

Fig. 9 Physical components of MEMS Pirani gauge .......................................8

Fig. 10 Sample Pirani gauge pressure vs. voltage model...................................9

Fig. 11 Manufacturer-produced pressure vs. voltage graph...............................9

Fig. 12 Sample Wheatstone bridge circuit configuration.................................11

Fig. 13 Die connections for a PTCD10 resistor ...............................................12

Fig. 14 Wheatstone bridge test: circuit diagram ..............................................12

Fig. 15 Wheatstone bridge test: breadboard implementation...........................13

Fig. 16 Wheatstone bridge test: test package in temperature chamber............13

Fig. 17 Thermal fluctuation experiment results...............................................14

Fig. 18 Sample heating profile for high vacuum sealing .................................16

Fig. 19 Sample Suss SB8e recipe for Au-Sn eutectic bonding ........................17

Fig. 20 Heating profile design iterative process...............................................17

Fig. 21 Optical photograph of a poor and good preform bond ........................21

Fig. 22 Suss SB8e temperature profile for the lid sealing phase......................21

Fig. 23 Overall Suss SB8e heating profile for submilliTorr vacuum 

packaging .............................................................................................23

Fig. 24 RGA experiment setup.........................................................................24

Fig. 25 RGA output for a 1-h bake out at T = 225 °C......................................25

Fig. 26 RGA output of a 2-h sample for an 8-h bake out.................................26

Fig. 27 RGA output of preform melting ..........................................................27

Fig. 28 RGA output of heating superglue ........................................................28

Fig. 29 Q-factor determination: experimental setup ........................................29

Fig. 30 Q-factor drive and sense mode: RF-C12 at 40 Torr ............................30

Fig. 31 Q-factor drive mode: RL-C11 at 3 Torr...............................................30
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Fig. 32 Q-factor drive mode: RL-C11 at 100 mTorr........................................31

Fig. 33 Empirical relationship between quality factor and pressure for QMG 

(Prikhodko et al. 2013) .......................................................................32

List of Tables

Table 1 Data output from Wheatstone bridge experiment................................15

Table 2 Heating profile design test specimens..................................................18

Table 3 Suss SB8e package bake-out experimentation results.........................19

Table 4 Suss SB8e bake-out parameters used to obtain package pressure of 3 

Torr ......................................................................................................19

Table 5 Suss SB8e ramp-up parameter used to obtain a package pressure of 3 

Torr ......................................................................................................20

Table 6 Suss SB8e lid seal parameter used to obtain a package pressure of 3 

Torr ......................................................................................................22

Table 7 Suss SB8e cool/purge parameter used to obtain package pressure of 3 

Torr ......................................................................................................22

Table 8 RGA experiment test specimens and outgassing properties................24
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INTENTIONALLY LEFT BLANK.
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1

1. Introduction/Background

There has been a growing need in society today for objects that humans use, both 

militarily and commercially, to be durable, faster, and efficient. From tanks and 

automobiles to unmanned aerial vehicles (UAVs) and robots, the need for improved 

performance is ubiquitous. Electronic sensors are no exception. In recent years, 

there has been a substantial amount of time and money invested in improving the 

performance and operability of position, navigation, and timing (PNT) systems. 

These systems need to be lighter, cheaper, and more power efficient to match the 

growing global dependence on them. In the defense sector, such devices should be 

able to match the various constraints and performance criteria of air and land robots, 

munitions, and constrained vehicle platforms. Currently, the standard navigation 

system that the US military uses is GPS. However, one of the drawbacks of GPS is 

its inherent weak signal and vulnerability to jamming by natural and unnatural 

means. This sole dependence on GPS technology may prove to be catastrophic if 

the signal is lost or broken. As such, development of microelectromechanical 

system (MEMS) inertial sensors that can provide navigation-grade performance can 

alleviate the military’s reliance on a single PNT. 

This report focuses primarily on improving the performance of one PNT system, a 

resonant quadruple-mass gyroscope (QMG), which has been manufactured inhouse by the US Army Research Laboratory (ARL) in Adelphi, Maryland.

1.1 Overview of MEMS Gyroscopes

Gyroscopes are one of the most important position sensors out in today’s market. 

A gyroscope is an in situ physical sensor that can detect and measure angular 

motion in an inertial reference frame. By being an in situ sensor, or measuring 

within itself, the gyroscope can measure absolute motion without relying on an 

external reference or signal. If 3 gyroscopes are combined with 3 accelerometers, 

another in situ physical sensor, a 6-axis inertial measurement unit (IMU) can be 

produced (Trusov 2011). A powerful PNT system, IMUs can be commonly found 

on most autonomous or intelligent systems, such as quadrotor helicopters and cell 

phones.

Gyroscopes are commonly divided into 3 categories: angle (or whole angle or rate 

integrating) and rate. Like the name suggests, angle gyroscopes measure absolute 

angular position. Similarly, rate gyroscopes measure absolute angular rates. The 

most common type of gyroscope being developed and manufactured today is the 

silicon vibratory rate gyroscope. An example of such a device is the ARL-fabricated 

QMG, shown in Fig. 1. The QMG was designed at the University of California, 
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Irvine under the Defense Advanced Research Projects Agency program. The design 

uses 4 silicon spring-suspended masses moving anti-phase from one another in the 

same plane of the chip to detect rotation angle out of plane of the chip (Trusov et 

al. 2014). What is unique about the device is that the QMG can not only operate as 

a rate gyroscope, but it has the capabilities to operate as a whole-angle device as 

well. Although in its infancy stages in performance determination and optimization, 

the potential for the QMG to be a powerful and efficient gyroscope is limitless. 

Fig. 1 ARL-fabricated QMG

In the past few decades, sensors and electronics have seen a rapidly diminishing 

form factor in terms of size. The current paradigm can be seen in MEMS becoming

smaller, lighter, and faster. Physically, MEMS devices have a diminutive form 

factor ranging from 0.1 to 1,000 μm in any dimension. With the current trend in 

technology development, the future holds for devices to be manufactured within 

the nano regime, as seen in Fig. 2. However, if nanotechnology is indeed the 

technology of the future, then MEMS is the technology of today (Fan 1988).

Fig. 2 Size of various devices following the technology trend
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Evidently, MEMS technology has seen its infusion into gyroscopes, particularly 

silicon-based vibratory rate gyroscopes, due to strong ties with semiconductor 

technology. Due to their size, power requirements, and cost, MEMS gyroscopes 

have become a particular favorite in various motion-detecting applications, such as 

consumer electronics and automotive safety devices (Trusov 2011).

1.1.1 Performance Parameters

A simple analytical model of a single-axis vibratory rate gyroscope is shown in 

Fig. 3. A rate gyroscope operates with nonsymmetry between the drive mode and 

sense mode, the x and y axes, respectively. The drive mode is driven into forced 

vibration mode with a prescribed amplitude and angular frequency. The sense mode 

acts to suppress the driven vibrations and can be used to measure input rate (Trusov

2011). Through this vibration feedback, a MEMS gyroscope acts as a resonant 

system.

Fig. 3 Theoretical model of a single z-axis vibratory gyroscope

There are numerous systematic parameters that characterize MEMS gyroscope 

performance. These parameters include scale factor, bandwidth, bias, and quality 

factor (Q-factor). In particular, this report looks into ways of improving Q-factor 

through vacuum packaging.

Q-factor is arguably the most important performance parameter. As mentioned 

earlier, the amount of vibration transferred from the drive to sense axis is dictated 

by the Coriolis force produced. The Coriolis force and, hence, the amplitude of the 

sense axis vibration, is proportional to the rotation rate (Leland 2005). Furthermore, 

it is also directly proportional to the Q-factor of the mode-matched gyroscope as 

seen by Eq. 1:

yy0mmmmmmmmheeee = Ωzz

2QQssxxoomm

mmssωωss

. (1)

Z, ζ Ω

y

η

Ψ

ξ

m x

k
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Q-factor is defined as the ratio between the amount of stored energy the gyroscope 

has to the amount of energy dissipated out per radian (Prikhodko et al. 2013). 

Ideally, the most efficient gyroscope would have a Q-factor of infinity, directly 

correlating to zero dissipated energy. However in reality, it is impossible to achieve 

such value. The benefit of high Q-factors is improved noise resolution and higher 

measurement sensitivity. Thus, when a PNT platform requires high precision and 

accuracy, high Q-factor gyroscopes are needed. 

To look at the importance of Q-factor to package pressure, it is important to analyze 

the empirical equation governing Q-factor, represented by Eq. 2 (Kim, et al. 2006):

1

QQ tt

= 1

QQ aaaa

+ 1

QQTTTTTT

+ 1

QQ aa hoo

+ 1

QQoo hee

. (2)

For a packaged system in a moderate vacuum pressure, if we assume thermal 

elastic dissipation to be negligible and ignore anchor loss and other, Eq. 2 can be 

simplified to 

1

QQ tt

≈ 1

QQ aaaa

. (3)

Air damping can be modeled for these microscale resonating structures by Eq. 4, 

which can be approximated to be proportional to square root of temperature over 

package pressure as seen by Eq. 5:

QQaaaaaa = h�

ππ

2�

2.5

ρρρρ�kkbbTT

mm

pp . (4)

QQaaaaaa ∝ √TT

pp . (5)

If temperature is fixed, it can be seen by linking Eq. 5 with Eq. 4 that low package

pressures will result in high total Q-factors.

1.2 Vacuum Packaging Overview

Packaging is one of the most important and expensive steps in the life cycle of 

MEMS manufacturing. On average, packaging takes up between 30%–70% of the 

total manufacturing cost. In terms of functionality, the purpose of packaging is to 

protect, power, and cool microelectronic chips or components while providing 

mechanical and electrical connections to the outside world. Furthermore, many 

MEMS packages require additional considerations such as a hermetic seal and 

vacuum encapsulation (Chiao et al. 2002). For MEMS gyroscopes, these additional 

requirements are warranted as a device’s performance increases in a vacuum 
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5

environment and the resonator does not want to be exposed to a phenomenon 

known as stiction due to high concentrations of moisture.

With the general demand of high-performance gyroscopes, the industrial trend over 

the past few decades is finding ways to improve vacuum packaging performance. 

Figure 4 illustrates this trend linking systematic performance parameters of Qfactor and bias with manufacturing cost for various industry demand regimes 

(Prikhodko et al. 2013). Although the most precise gyroscopes are the most 

expensive, future trends in vacuum packaging design will have substantially lower 

costs with very little loss in performance.

Fig. 4 MEMS gyroscope performance vs. cost tradeoff

1.2.1 General Packaging Procedure

There are numerous MEMS gyroscope packaging procedures in the scientific 

community. Although each procedure was developed for a unique piece of 

hardware, all share the same common engineering strategy when it comes to 

vacuum packaging. Figure 5 depicts a block diagram of the overall packaging 

procedure.

Fig. 5 Overall MEMS vacuum packaging procedure
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1.2.1.1 Bake Out

Bake out is the first step in any packaging sequence, although it does not happen 

during vacuum packaging itself. The goal here is to remove any residual species 

that might become trapped inside of package. For example, a significant amount of 

hydrogen can become trapped in the electroplated metal coating on the package,

making the package itself a major source of outgassing (Schofield et al. 2010). The 

general practice used to remove potentially trapped species is to bake out the 

package in a high-temperature and ultra-high vacuum environment. An example of 

such can be a 1-h bake out at 400 °C and 1×10–6 Torr.

1.2.1.2 Die Attachment

After baking out the package, the MEMS die itself must be attached to the package. 

The die can be attached using a solder preform or an adhesive such as Kapton tape. 

The goal here is to provide a strong bond between the package and die with little 

stress and as little potential for outgassing as possible. An example solder preform 

used is 80/20 gold (Au)-tin (Sn) due to its low eutectic melting temperature of 

280 °C and its low outgassing properties. An example die attach schematic is shown 

in Fig. 6.

Fig. 6 Example die attachment schematic

1.2.1.3 Wirebond

In order for the MEMS die to connect electrically with the package or other 

electrical devices inside of the package, the die must be wirebonded to the 

respective component. Typically, an industrial wirebonder is used in order to 

produce precise and low-stress attachment points with either ball, wedge, or 

compliant bonding types. The bond wires are always metals and can range from 

aluminum to Au composition. An example wirebond can be seen in Fig. 7 where 

the MEMS die is connected to the package itself.
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Fig. 7 Example wirebond between MEMS die and package

1.2.1.4 Vacuum Sealing

Vacuum sealing is the final step in the packaging process. The goal here is to ensure 

the lid bonded to the package provides a hermetic, airtight seal. Before the final 

seal is attached, all components must go through a final bake out to remove any 

residual species that may have been introduced during die attachment and 

wirebonding steps. In order to fully remove these species, a specifically designed 

getter will need to be activated in order to absorb and remove them. Depending on 

what types of species need to be removed, different getter materials are chosen. For 

example, a getter made out of a desiccant or polymer material will target and 

remove moisture from the package. The polymer will form hydrates when reacting 

with water and will act as a quasi-pump when drying out the package. To transition 

to the sealing stage, the lid must be lowered and aligned properly with the package. 

Finally, the lid is bonded directly to the package by melting of the preform. Similar 

to the die attach preform solder, 80/20 Au-Sn is widely chosen as the lid preform 

material. Figure 8 show a post-packaging sealing where the sealing lid is the last 

component added in the packaging process

Fig. 8 Post-packaging vacuum lid seal
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1.3 Pirani Gauge Overview

For MEMS gyroscopes, maintaining a proper hermetic seal is vital for both the 

performance and longevity of the device. The seal is maintained through the 

monitoring of the internal package pressure. Typical monitoring techniques include 

a helium leak rate test as well as pressure extracted from the Q-factor. Although 

these accepted techniques do provide insight into status of hermetic seal, they 

require a laborious test setup and expensive equipment, and cannot observe minute 

changes in pressure. Another cost-effective and efficient method is using Pirani 

gauges. These Pirani gauges provide in situ measurements of internal package 

pressure without compromising the integrity of the seal through destructive testing. 

They are manufactured small enough to fit into virtually any package and can be 

placed in an array setup to provide a high-resolution measurement of the package 

pressure.

Pirani gauges are suspended resistors in which heat loss provides a measure for the 

surrounding pressure (Santagata et al. 2010). Typically, Pirani gauges specific for 

MEMS applications are manufactured to operate in a variety of low-pressure 

environments (Topalli et al. 2009). Figure 9 illustrates the basic fundamentals on 

how a Pirani gauge operates. 

Fig. 9 Physical components of MEMS Pirani gauge

When a current, I, is applied to the gauge and passes through the bridge, the 

temperature of the gauge increases; thus, the resistance changes. As the temperature 

increases, heat is transferred, conductively and convectively, from the bridge to the 

substrate via anchors and gas within the gap g. As the pressure of the Pirani gauge 

changes, the conductance of the gas changes as well. This can be easily seen 

through the definition of thermal conduction. Since resistance is defined as the 

inverse of conductance, if the conductance of the gas changes, the resistance of the 

Pirani gauge would change as well. Thus, the measurement of voltage across the 

bridge of the Pirani gauge is a direct indication of pressure. This relationship can 

be simply modeled by Ohm’s Law:

VV(pp) = IIII(pp). (6)
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There have been theoretical models developed for Pirani gauges that try to expand 

upon the simple relationship outlined by Eq. 6. In general, any expansion done will 

leave the equation transcendental in nature. To overcome this, transfer functions 

are required. For simplicity, this report does not use an analytical model for 

determining package pressures, but uses calibration curves to determine pressure 

given a voltage reading. Both approaches generate voltage versus pressure curves 

that are S-shaped in nature. Figure 10 illustrates a sample analytical model and 

Fig. 11 illustrates a manufacturer-tested Pirani gauge calibration curve.

Fig. 10 Sample Pirani gauge pressure vs. voltage model

Fig. 11 Manufacturer-produced pressure vs. voltage graph

2. Experimental Approach

To achieve the engineering goal of improving QMG performance through a novel 

vacuum packaging process, the complete packaging process was analyzed and 
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dissected into 3 main categories: in situ pressure gauging, heating design, and 

outgassing analysis. Each category has the same theme in mind: finding ways to 

accurately determine pressure and reduce it. Within each of the 3 categories, a series 

of experiments was conducted that directly correlated and contributed to the 

universal theme. These experiments were designed based on an extensive literature 

review on the subject of vacuum packaging. 

2.1 Thermal Fluctuation Experiment

Thermal fluctuation is defined as the perturbation a thermodynamic system 

undergoes from its equilibrium state. Generally, thermal fluctuation is primarily 

influenced by temperature as a gradient of temperature acting on a system can cause 

perturbation to that system both macro- and microscopically. For Pirani gauges, 

keeping a steady temperature is essential for accurate measurements of pressure 

through voltage readings. When testing in a lab environment, it is very hard to 

control the ambient room temperature as there are a plethora of heat sources and 

sinks within the laboratory itself. The physical effect of thermal noise on a Pirani

gauge can be seen in the change in conductance. Through Fourier’s Law for 1-D

thermal conductance, the local heat flux can be related to the differential in 

temperature scaled by the material’s thermal conductivity by Eq. 7 (DeWitt and

Incropera 1953):

qqxx = −kk dd

dd . (7)

If Eq. 7 is integrated around the gauge’s surface area, AA, and the gauge is assumed 

to be composed of homogenous material, uniform kk, one can obtain Eq. 8:

∆QQ

∆tt = −kk ∆TT∆xx

. (8)

We can tie Eq. 8 to conductance through its relationship with resistance. From 

Pouillet’s Law, Eq. 9, electrical resistance is proportional to electrical resistivity, ρρ, 

of the gauge and length of bridge, xx, while inversely proportional to the bridge’s 

cross-sectional area, AA:

= ρρ xx

AA

. (9)

By definition, electrical conductance, GG, is defined as the inverse of electrical 

resistance and can be written as 

GG = 1

RR = kkxx . (10)
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For heat transfer, conductance, UU, can be written in a similar form as Eq. 10:

UU = kk

∆xx

. (11)

Substituting Eq. 11 into Eq. 8 and simplifying using inverse relationship between 

conductance and resistance, a simple relationship between temperature and heat 

transfer per unit time can be generated:

= ∆TT

QQ̇

. (12)

For temperature fluctuations across the Pirani gauge, the resistance of the gauge 

changes accordingly. Applying Ohm’s Law, one can see that a change in pressure 

coupled with a constant prescribed current will cause changes in voltage 

measurements across the gauge. As a result, thermal noise is added to the voltage 

readings, thus making the task of precisely measuring pressure onerous. One 

possible solution to this problem is directly controlling the temperature in a 

temperature chamber. However, due to the immobility of such a device, it does not 

provide a flexible solution to mitigating thermal fluctuations. Instead, a widely 

practiced routine used by Pirani gauge manufacturers is a Wheatstone bridge 

configuration.

Bridge circuits are the most common method of connecting passive transducers to 

measuring systems. One of the most widely implemented bridge circuits is the 

Wheatstone bridge configuration devised by SH Christie in 1833 (Beckwith et al. 

1995). An example of a DC Wheatstone bridge configuration is shown in Fig. 12.

Fig. 12 Sample Wheatstone bridge circuit configuration

Typically, one or more of the resistors, shown in Fig. 13, are of unknown value and 

through the balancing of the bridge, vvoo = 0 VV, the value can be determined. For a 

Pirani gauge, the goal of a Wheatstone bridge configuration is to shunt temperatureinduced resistance fluctuations and allow for more accurate measurements of the 

gauge voltage. Using a voltage-feedback loop connected to the bridge, the 
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12

resistance of one of the known legs can be fine-tuned to nullify gauge resistance 

perturbation and maintain a balanced bridge.

Fig. 13 Die connections for a PTCD10 resistor

For this experiment, a thermal gas conductivity sensor die PTCD10, manufactured 

by Posifa Microsystems Inc., was used as the pressure sensor. Although not an 

integrated Pirani gauge with a bridge configuration, the die was chosen due to its 

diminutive size and its ability to be wirebonded to the package itself. The die 

consists of 2 thermally dependent resistors, as shown by Fig. 12. The reference 

resistor allows for reference of an on-chip voltage change, which directly correlates 

to a temperature such that the pressure change can be thermally isolated.

When designing the Wheatstone bridge setup for the PTCD10, it was important to 

note that 2 legs of the bridge, the measurement resistor and the reference resistor,

would need to be shunted to remove thermal fluctuations from the voltage 

measurements. Furthermore, the shunting would require a differential resistor; thus, 

potentiometers were implemented. The circuit diagram that was implemented 

during testing is shown in Fig. 14 and the actual setup is shown in Figs. 15 and 16.

Fig. 14 Wheatstone bridge test: circuit diagram

A

B

C

D
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13

Fig. 15 Wheatstone bridge test: breadboard implementation

Fig. 16 Wheatstone bridge test: test package in temperature chamber

Three voltmeters (Vapplied, Vbridge, Vsense) were used to measure the voltage across 

the entire setup, the bridge, and the measurement resistor, respectively. A DC 

constant-current bridge approach was implemented, instead of a DC constantvoltage bridge, to regulate current throughput through the die. The current through 

each leg can be determined using Kirchoff’s current divider law. The resistance 

values of R2 and Rpot were chosen based on a sensitivity analysis of ∆VVaaaa, where the 

goal was to make ∆VVaaaa → 0 VV given 3 = 4, ∆ 3 = ∆ 4 = ∆ , and VVbb = 0 VV. 

Equation 13 shows the mathematical sensitivity of ∆VVaaaa and Eq. 14 shows the 

theoretical value for Rpot to maintain a balanced bridge:

VVaaaa + ∆VVaaaa =

II� 1

RRpp

+ 1

RR +∆RR�

−1

� 1

RR4 + 1RRss ss +∆RR�

−1

+ � 1

RRpp

+ 1

RR +∆RR�

−1 ��

1

RR4

+ 1

RRss ss +∆RR

�

−1

+ 3�.(13)

pp = � 1

RR4

+ 1

RRss ss

− 1

RR �

−1

. (14)

The test setup consisted of a temperature chamber that was set to 4 static room 

temperature values: 15, 20, 25, and 30 °C. The current source was set to a range of 

values (15, 25, 35, 45, 55, and 65 mA) that prescribed between 2–10 mA through 
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14

the measurement resistor. Based off sensitivity analysis, the resistors were chosen 

to be 2 = 50 Ω, 3 = 4 = 100 Ω, and pp = 40 Ω. The potentiometer was 

calibrated initially at 15 °C, 15 mA and stayed static throughout experiment. The 

result of the experiment is shown in Fig. 17. Table 1 highlights the prescribed 

current values through the measurement resistor, theoretical potentiometer 

resistance, and percent error from the static potentiometer value. 

Fig. 17 Thermal fluctuation experiment results
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Table 1 Data output from Wheatstone bridge experiment

Temp 

(°C)

DC current 

(mA)

Isense

(mA)

Rpot

(theoretical) (Ω)

% error 

(Rpot)

15

15 2.185 40.712 0.52%

25 3.645 40.712 0.52%

35 5.129 40.712 0.52%

45 6.622 40.712 0.52%

55 8.132 40.712 0.52%

65 9.666 40.712 0.52%

20

15 2.168 40.796 0.73%

25 3.619 40.796 0.73%

35 5.087 40.796 0.73%

45 6.562 40.796 0.73%

55 8.063 40.796 0.73%

65 9.588 40.796 0.73%

25

15 2.153 40.870 0.91%

25 3.589 40.870 0.91%

35 5.041 40.870 0.91%

45 6.509 40.870 0.91%

55 7.993 40.870 0.91%

65 9.502 40.870 0.91%

30

15 2.139 40.937 1.07%

25 3.559 40.937 1.07%

35 5.004 40.937 1.07%

45 6.457 40.937 1.07%

55 7.934 40.937 1.07%

65 9.427 40.937 1.07%

From the results, it can be seen that the Wheatstone bridge setup produces an ideal 

shunting of temperature-induced voltage fluctuations across the measurement 

resistor of the PTCD10 die. The slope of the plots generated in Fig. 17 shows that 

at best the bridge setup can guarantee a stable, unhindered voltage reading of 

±0.2 mV per 1 °C fluctuation. Furthermore, with increasing applied current, the 

voltage reading sensitivity increases slightly but is small in comparison with 

voltage sensitivities without the bridge configuration. Table 1 suggests that 

swapping a static 40-Ω resistor with a potentiometer will provide sufficient 

resistance to balance the bridge as there is a less than 1% error in potentiometer 

resistance. Nevertheless, the Wheatstone bridge design will provide for more 

precise measurement of the Pirani gauge voltage values and thus allow for more 

accurate characterization of the internal package pressure.
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2.2 Heating Profile Design

Heating profile is at the center of the packaging process. It defines the physical 

process for which a package is hermetically sealed in a vacuum environment. A 

heating profile is a temperature versus time plot of the complete packaging process

and is typically produced by a packaging machine. An example heating profile that 

outlines the major packaging steps can be seen in Fig. 18 (Prikhodko et al. 2013). 

A well-designed heating profile can make the difference between a moderate 

pressure package and an ultra-low vacuum package.

Fig. 18 Sample heating profile for high vacuum sealing

The heating profile designed that this report discusses was created using Suss SB8e 

wafer bonder manufactured by Suss Microtech. The bonder was set up for preform 

eutectic bonding with a transport fixture that allows for spacer/clamp actuation. The 

system uses a graphical user interface (GUI) that allows the operator to create the 

heating profile, or what Suss calls “recipe creation”. An example recipe for Au-Sn 

wafer bonding is shown in Fig. 19.
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Fig. 19 Sample Suss SB8e recipe for Au-Sn eutectic bonding

As shown in Fig. 19, the recipe editor allows for numerous system parameters to 

be controlled, including temperature of the top and bottom heating plates, chamber 

pressure, tool pressure, spacer/clamp/tool actuation, log time, and wait time for 

each step.

As outlined in Section 1.2.1, the heating profile was designed based off the 4 main 

steps of vacuum packaging. Each step begins with a baseline approach found from

literature review on the subject, and through iteration, the step is optimized until 

desired performance is achieved, as shown by Fig. 20.

Fig. 20 Heating profile design iterative process

Tool Control

Spacer Actuation
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It is important to note that these baseline approaches are not universal to all vacuum 

packaging systems and are directly dependent on what system is being used. It only 

provides guidance or a starting point to where testing on a Suss machine should 

begin. The primary materials used in the heating profile design, excluding the Sussmanufactured parts, are listed in Table 2.

Table 2 Heating profile design test specimens

Component name Material info

Ceramic package Kyocera A-440 (sapphire [Al2O3]), electroplated 

nickel (Ni) and Au

Lid Kovar, electroplated Ni and Au

Preform 80/20 Au-Sn

Superglue Ethyl cyanoacrylate

PTCD10 die Pirani gauge

QMG Silicon-based

2.2.1 Bake Out

A substantial amount of literature provide various recommendations for bake-out

schematics. The general range of bake-out temperatures in a vacuum environment 

for eutectic bonding goes from as low as 50 °C to as high as 400 °C (Paquet et al.

2013). One of the primary concerns with low-temperature bake outs (50–200 °C)

is the time required to drive out trapped hydrogen gas in electroplated lid and 

package, which is on the order of weeks to months. On the other side of the 

spectrum, a temperature higher than 350 °C is needed in order to drive hydrogen 

from iron-based alloys. Although the bake-out time is substantially reduced, a 

consequence of the high temperature is a reduction in wire bondability due to 

surface Au diffusion and reaching the preform’s eutectic point. It is suggested that 

an optimized bake out be done at 250 °C for 1 week to nullify evolved hydrogen 

concentrations. However, empirical data suggests that a bake out at 400 °C for 1 h 

without the preform attached to the lid provides similar results (Ramesham 2004).

Using these 2 aforementioned suggestions, tests were conducted to determine 

which setup would yield to a lower package pressure. Due to onerous suggested 

time of 1 week (168 h), the 250 °C bake-out temperature was tested at 48 and 72 h, 

trials 1 and 2, respectively, initially in order to determine if increasing bake-out

time does lead to lower package pressures. These tests were conducted with the 

package, lid, and preform, where spacers were implemented to displace the preform 

and lid from the package. Table 3 outlines the results from the experimentation, 

which shows that increasing time duration at 225 °C did improve internal package 

pressure, but not substantially. 
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Table 3 Suss SB8e package bake-out experimentation results

Trial 

no. Components Temperature 

(°C)

Chamber 

pressure 

(Torr)

Duration 

(h)

Package 

pressure 

(Torr)

1 Lid + preform, package 225 4.E-05 48 20

2 Lid + preform, package 225 4.E-05 72 18

3 Package 4004.E-05

1

6

Lid + preform, package 225 48

In order to test the 1-h, 400 °C suggestion, trial 3, the package needed to be baked 

out separately from the lid and preform to avoid the preform’s eutectic point. 

Furthermore, using a similar setup as the previous 2 trials, the package was rebaked 

with the lid and preform after tests for wire bondability were conducted. The results 

shown in Table 3 along with residual gas analyzer (RGA) readings not only confirm 

the empirical data suggestion, but provide insight into the importance of baking 

components separately initially before vacuum-seal bake out, as seen by the 

substantial reduction in package pressure. 

From these trials, the final bake-out parameters for testing on packaging a QMG 

were determined as shown in Table 4. The parameters are almost identical to trial 

3 with the addition of baking out the lid separately. The result of this addition is a 

considerable reduction in package pressure to 3 Torr. Due to time constraints, more 

testing and optimizing of bake-out parameters could not be accomplished. 

However, the preliminary results from the bake-out design provide important 

insight into what parameters drastically improve packaging pressure as it moves 

into the desired submilliTorr regime.

Table 4 Suss SB8e bake-out parameters used to obtain package pressure of 3 Torr

Heating 

profile 

step

Components Temperature 

(°C)

Chamber 

pressure 

(Torr)

Duration 

(h)

Package 

pressure 

(Torr)

Bakeout

Package 400

4.E-05

1

Lid + preform 225 12 3

Lid + preform , package 400 48

2.2.2 Ramp-Up

Ramp-up is the step where entire package suite is heated from its bake-out

temperature to a maximum heating profile temperature, typically greater than the 

preform’s eutectic melting temperature. The goal of this step is to ensure the 

eutectic temperature of the preform is reached while setting up the lid for bonding 

with the package. A ramp-up can be accomplished either linearly, by setting the 

end temperature and allowing the bonding system to reach it on its own, or 
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piecewise, where the operator defines temperature values to be met and steps up to 

the end temperature. One of the most important driving factors for the designed 

ramp-up’s performance is heat transfer. In a low-vacuum environment, the most 

dominant type of heat transfer is radiation. Radiation heat transfer between 2 

objects can be modeled by Stefan-Boltzmann equation, Eq. 15, where QQ is the heat 

flux, εε is the emissivity of the object, σσ is Stefan-Boltzmann constant, and TT is the 

temperature of the object:

QQ = εε �TT1

4 − TT24�. (15)

For a perfect blackbody, εε = 1; however, in most cases, the material used in 

vacuum packaging will have a εε < 1. As a result, the only mathematical way to 

transfer a lot of energy in the form of heat from body 1 to body 2 is to have body 1 

be as hot as possible and body 2 be as cool as possible. Relating this to the rampup design, the maximum heating profile temperature will need to be substantially 

larger than the preform’s eutectic melting temperature in order to guarantee the 

preform melting in an ultra-low-vacuum environment.

To have more user control over the ramp-up, a piecewise approach was 

implemented in the experimentation. During the beginning of the ramp-up, spacers 

were actuated to lower the lid and preform onto the package and a wafer bonder 

tool was lowered to provide weight on the lid. Using the aforementioned bake-out

temperature, the Suss SB8e was programmed to reach a maximum temperature of 

425 °C in an ultra-low-vacuum environment. Through iteration, the value of 

a 425 °C was chosen to provide consistent eutectic melting and adequate time for 

the preform to reflow and solidify. In general, it was determined that temperatures 

above 400 °C were needed to reach the 278 °C eutectic temperature of 80/20 AuSn. Table 5 outlines the ramp-up parameters used to obtain a package pressure of 

3 Torr

Table 5 Suss SB8e ramp-up parameter used to obtain a package pressure of 3 Torr

Heating profile step Max temperature 

(°C)

Chamber 

pressure 

(Torr)

Temperature 

intervals 

(°C)

Duration 

(min)

Ramp-up 225 4.E-05 300, 350, 375 6

2.2.3 Lid Seal

Physically, lid seal is the point where the preform reaches its eutectic point, melts 

into liquid form, and bonds through solidification via reflow onto the package. One 

important consideration for lid sealing is bonding time. It is important to provide 

adequate time above the preform’s eutectic point to ensure proper bonding between 
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21

the package and the lid. If not enough time is given, the preform may not reflow 

enough to provide a hermetic seal and thus compromise the integrity of the vacuum 

package. An example of a poor bond is shown in Fig. 21, where the result of the 

bond was a complete loss in vacuum pressure of the package despite the preform 

melting to the package.

Fig. 21 Optical photograph of a poor and good preform bond

The designed lid seal operates at 425 °C in a vacuum environment and was held for 

10 min to ensure, at a minimum, at least 5 min above the experimental testing 

melting temperature of the preform in Suss SB8e, namely, 400 °C. Figure 22 is the 

temperature output from the Suss SB8e for the lid sealing step, which validates that 

the minimum time-above-eutectic was satisfied. Table 6 outlines the lid seal 

parameters used to obtain a package pressure of 3 Torr.

Fig. 22 Suss SB8e temperature profile for the lid sealing phase

Preform Reflow

No Preform Reflow
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Table 6 Suss SB8e lid seal parameter used to obtain a package pressure of 3 Torr

Heating profile step Temperature 

(°C)

Pressure 

(Torr)

Duration 

(min)

Lid seal 425 4.E-05 10

2.2.4 Cool/Purge

The goal of cooling is to ensure proper reflow of the preform as it transitions from 

a liquid to a solid state and ensure proper cooling of the system in a low-vacuum 

environment. Like the ramp-up stage, cooling can be accomplished linearly or 

piecewise. Furthermore, to improve heat transfer, low nitrogen gas can be purged 

into the system (Prikhodko et al. 2013). 

To have more user-control over cooling, a piecewise approach was implemented in 

the experimentation. The system was gradually brought down in temperature while 

still in a low-vacuum environment. To prepare the package for removal, the wafer 

bond tool was actuated up and the system was purged. Table 7 outlines the 

cool/purge parameters used to obtain a package pressure of 3 Torr.

Table 7 Suss SB8e cool/purge parameter used to obtain package pressure of 3 Torr

Heating profile 

step

Min temperature 

(°C)

Pressure 

(Torr)

Temperature 

intervals 

(°C)

Cooling 

duration 

(min)

Purge 

duration 

(min)

Cool/purge 25 4.E-05 200, 150, 50 20 30

Through the iterative process in the heating profile design shown in Fig. 19, a 

consistent and repeatable vacuum packaging process was produced. The resulting 

package from the heating profile design is at a low pressure and is hermetically 

sealed. In addition, the implementation of spacers in the design sequence proved to 

be substantial in the performance of the design. Figure 23 depicts the overall 

heating profile design used to achieve a 3-Torr package pressure.
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Fig. 23 Overall Suss SB8e heating profile for submilliTorr vacuum packaging

2.3 Residual Gas Analyzer Experiment

The motivation behind vacuum packaging is not just centered on improving MEMS 

performance. One of the critical roles vacuum packaging has is providing internal 

component safety and longevity. A proper hermetic seal will allow for MEMS 

devices to be thermodynamically isolated from the ambient operating environment. 

This, in turn, reduces any potential for life-time degradation of the device. It is also 

important to remove any outgassed or residual species from the package before it 

is sealed. Similarly, a proper vacuum package will negate any potential for harmful 

species to interact with the device. In view of the latter point, an RGA experiment 

was conducted in order to analyze outgassing and residual species during the 

heating profile design and provide insight into outgassing mitigation techniques.

An RGA is a small, rugged mass spectrometer used in process control and 

contamination-monitoring of vacuum systems. It is used in most cases to measure 

the quality of the vacuum and can measure extreme vacuums as low as 

10–14 Torr. An RGA works on the principle of mass-to-charge ratios where a small 

fraction of incoming gas molecules are positively ionized and the resulting ions are 

separated, detected, and measured according to their molecular mass (Stanford 

Research Systems 2009).

For this experiment, the Pfeiffer Prisma 80 QME-200 RGA was hooked up to a 

pressure-tap valve on the Suss SB8e wafer bonder as shown in Fig. 24. A manual 

control-valve was also installed to control the vacuum pressure going to the RGA 
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24

as the specific RGA implemented can operate in vacuum conditions of 1×10–4 mbar 

(7.5×10–5 Torr) or less. The materials used in the experimentation were the same as 

materials used in the heating profile design. Additionally, a literature review was 

conducted on component-specific materials and their key outgassing properties in 

high-temperature vacuum environments. These chemical properties were used as 

quality checks for the experiment. The list of test components and their outgassing 

properties are listed in Table 8.

Fig. 24 RGA experiment setup

Table 8 RGA experiment test specimens and outgassing properties

Component name Material info Outgassing properties

Ceramic package Kyocera A-440 (Al2O3), electroplated 

Ni and Au

Low CTE, traps H2 and moisture

Lid Kovar, electroplated Ni and Au Traps H2 and moisture

Preform 80/20 Au-Sn Release CO2 when melting

Superglue Ethyl cyanoacrylate Releases NOx, CO, CO2 when 

heated

PTCD10 die Pirani gauge N/A

QMG Silicon-based N/A

The results for the experiment not only validate the outgassing properties for each 

component, but provides insight into the major species present during the vacuum 

sealing process. During the bake-out step of the heating profile design, the primary 

species the RGA read was water vapor, as shown by Fig. 25. Water vapor is 

arguably one of the hardest molecules to remove from any vacuum system. Despite 

only constituting a minute concentration of around 4% in air at 1 atm and 20 °C, 

water vapor contributes a 7 Torr partial pressure and is dependent on the humidity 

levels of the air (Ramesham 2004). Through opening and closing the vacuum 

system door, the vacuum became exposed to ambient air and thus water vapor was 

reintroduced into the system. At low-pressure environments, water vapor becomes

the dominant species in terms of partial pressure. The polar nature of water 
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25

molecules not only causes them to adhere to surfaces with weak bonds, but adhere 

to one another, thus creating layers of collected moisture (Danielson 2001). For a 

1-h bake out, the readings indicate that the increasing concentrations of water come 

from trapped moisture outgassed from the electroplated package itself. 

Furthermore, the expected high concentration of water initially is a direct indication 

of the importance of baking out the vacuum chamber to remove residual layers of 

moisture before the heating profile can commence. 

Fig. 25 RGA output for a 1-h bake out at T = 225 °C

To reduce these water concentrations over time, a longer bake out is needed. As 

shown by Fig. 26, an 8-h bake out is sufficient to drive down water concentrations

as measured by RGA.
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Fig. 26 RGA output of a 2-h sample for an 8-h bake out

The average H2 concentration for an 8-h bake out was measured to be 0.0306%, 

which indicates the need for even longer bake outs to reduce H2 concentration 

levels. Literature indicates bake outs on the order of 2–7 days at 250 °C are 

sufficient to reduce H2 concentration levels. Nevertheless with a 48-h bake-out test 

conducted in the heating profile design, the average H2 concentration was measured 

to be 0.00013%. This reduction in evolved hydrogen confirms the bake out’s 

performance in removing trapped H2 in the electroplated lid and package.

The presence of CO2 was noted during the eutectic melting of the preform. As in 

any combustion reaction with excess oxygen, CO2 is always a product. Figure 27

shows this phenomenon through the increase in CO2 and the reduction in O2.
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Fig. 27 RGA output of preform melting

Lastly, the RGA was able to confirm the outgassing of inorganic molecules (CO2, 

CO, NOx) from the heating of the superglue used to tack the PTCD10 die to the 

package. For the test depicted in Fig. 28, an excess amount of superglue was 

implemented. The result was a consistently elevated concentration of 

approximately 15% throughout the test duration. In actual implementation, not as 

much superglue would be implemented to bond the Pirani gauges. However, the 

key finding that this experiment demonstrates is the high outgassing from 

superglue. As ethyl cyanoacrylate is heated, it vaporizes very quickly into various 

organic molecules and compounds. Therefore, these compounds must be mitigated 

through an extensive bake out to avoid being trapped inside the sealed package. An 

alternative adhesive to superglue would be using Kapton tape. The tradeoff to using 

Kapton tape is although it has minute and negligible outgassing properties at 

elevated temperatures, it loses adhesive strength with increasing temperatures, thus 

increasing the potential for the Pirani gauge to become disconnected from the 

package surface, making wirebonding tedious. 
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Fig. 28 RGA output of heating superglue

In summary, the RGA output provides good insight into the physical chemistry that 

occurs during the heating cycle. Although this work does not deal with getter 

activation, the data will allow for a better selection of getter material. Furthermore, 

the reduction of residual species over time serves as a qualitative check on the 

designed heating profile steps as well as the packaging material selection. It was 

found through experimentation that the reduction in key trapped species directly 

correlated to reductions in internal package pressure. 

3. Results

The design methodology to measure Q-factor was centered on a frequency response 

of the gyroscope. For a resonating device such as a gyroscope, Q-factor is defined 

as the ratio of the resonant frequency, ffRR, to the half-power bandwidth, ∆ff, as 

shown by Eq. 16. A frequency response of the gyroscope will allow for both the 

resonant frequency and bandwidth to be determined.

QQ = RR

∆ . (16)

The gyroscope used throughout the entire vacuum packaging design and Q-factor 

determination was an in-house manufactured QMG, shown in Fig. 1. An 

experimental setup, as shown in Fig. 29, was created to conduct the frequency 

response. 
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Fig. 29 Q-factor determination: experimental setup

An analog network analyzer was implemented (top left image of Fig. 29) to serve 

as the function generator for the prescribed signals for the drive mode (x-axis) and 

sense mode (y-axis). In addition, the network analyzer was also set up to measure 

the frequency response spectrum of both modes and output the data for 

postprocessing Q-factor determination. Lastly, a DC power supply (top right image 

of Fig. 29) was additionally implemented to prescribe a DC voltage/current to the 

QMG capacitors.

Q-factor for 2 QMGs were measured after vacuum packaging using the 

aforementioned experimental setup. One QMG, labeled RFC-12 in the bottom right 

image of Fig. 29, was previously packaged using an SST International 3130 

Vacuum Furnace with a known internal package pressure of 40 Torr. The RFC-12 

QMG served as a baseline/control for comparison with Suss SB8e vacuum 

packaged QMGs. Nevertheless, the other QMG, labeled RLC-11 in bottom left 

image of Fig. 29, was packaged in the Suss SB8e using foundations laid down in 

Section 2 with an internal package pressure of 3 Torr. The frequency response 

showing the resonant frequency, bandwidth, and Q-factor for each QMG with their 

respected measured package pressure is shown in Figs. 30 through 32.
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30

Fig. 30 Q-factor drive and sense mode: RF-C12 at 40 Torr

Fig. 31 Q-factor drive mode: RL-C11 at 3 Torr
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Fig. 32 Q-factor drive mode: RL-C11 at 100 mTorr

As expected, it can be seen that reductions in package pressure from 40 to 

3 Torr directly correlate to significant increases in the gyroscope’s Q-factor from 

2,580 to 8,900. When packaging pressure was reduced to 100 mTorr, the resulting 

Q-factor was approximately 19,000. Furthermore, as expected, Q-factor calculated 

for the drive and sense modes of each package are nearly the same. Due to time 

limitations, this report was not able to expand this trend to ultra-low-vacuum 

packaged QMGs. However, future development expanding on this trend is expected 

to show relationships between Q-factor and package pressure, as seen by Fig. 33.

ARL results are superimposed on Fig. 33 and Q-factors are slightly higher at the 

same pressure than the QMGs used in Prikhodko et al (2013). ARL’s higher Qfactor is due to Prikhodko et al. (2013) use of a 100-μm-thick device layer, whereas 

the ARL QMGs are 40 μm thick. The thicker device layer will have higher squeeze 

film damping values and hence lower Q factor values.
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Fig. 33 Empirical relationship between quality factor and pressure for QMG (Prikhodko

et al. 2013)

4. Conclusions

The overall motivation for designing a novel vacuum packaging design process was 

to improve a MEMS QMG’s performance, in particular, its Q-factor. Through 

mathematical analysis and a literature review of Q-factor, it can found that Q-factor 

has a strong dependence on its operating environment’s pressure. By linking 

pressure to Q-factor, a series of experimental approaches were conducted with the 

goal of finding ways to accurately determine pressure and reduce it. Finally, to truly 

validate this relationship, Q-factor for the QMG was determined.

The results show that importance of vacuum packaging for MEMS gyroscopes 

should not be overlooked. A properly designed heating profile can allow for a low

packaging pressure to be obtained. The internal chemistry during the heating profile 

can be monitored using an RGA and, at the same time, can provide insight into 

performance of the heating profile and hermetic sealing. Although this report was 

unable to reach the packaging pressure goal of the submilliTorr regime, the data 

obtained from RGA will provide recommendations for future development such as 

the selection and implementation of getter material and cryogenic cooling to 

remove trapped water vapor inside the vacuum chamber. Through implementing an 

in situ approach while mitigating state function dependence, precise measurements 
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33

of internal vacuum pressure can be obtained. Putting all of these intertwined blocks 

together, the foundation of better-performing MEMS gyroscopes can be built. 

5. Future Work

Despite the novel vacuum packaging process that was developed for the MEMS 

QMG in this report, there are various other experiments that need to be conducted 

to complete the overall vacuum packaging cycle. Future work will look into 

methods of expediting the heating profile design time while ensuring the same or 

improved performance. Based off preliminary RGA data, getter material can be 

selected and introduced into the packaging procedure. Secondly, through the RGA 

data, it was concluded that the reason the developed heating profile was unable to 

generate submilliTorr packaging pressures was due to residual water vapor trapped 

inside the package. As residual water vapor is a major problem in a vacuum system, 

future tests will be conducted with the goal of removing trapped moisture from the 

vacuum system. Finally, tests will be conducted on the heating profile itself to make 

it universal to industrial vacuum systems.

The long-term stability of a hermetically sealed package is important for the 

lifetime of the packaged device. The vacuum packaging process developed 

provides the foundation for fabricating a hermetic seal. Future work will build upon 

this foundation and test for its long-term performance through helium leak-rate tests

that can be set to meet a certain minimum criterion. Furthermore, long-term 

stability of the seal will directly lead to long-term stability of the gyroscope’s Qfactor. As such, future work will also test packaged QMGs for their Q-factor days, 

weeks, and months after the completed packaging process. 

Other performance parameters of gyroscopes, such as bias stability and angle 

random walk, can be improved through a proper, stable vacuum package. As these 

gyroscopes with inevitably operate in dynamic environments, a proper packaging 

process must be developed to ensure long-term durability while increasing 

performance. Future work dealing with these other performance parameters will be 

conducted as well.
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6. References

Beckwith T, Marangoni R, Lienhard J. Mechanical measurements. 5th edition. New 

York (NY): Wiley; 1995. Vol 7, p. 272–281.

Chiao M, Lin L. Technical digest of solid-state sensor. Actuator and Microsystems 

Workshop, Hilton Head, SC, 2002 Jun; p. 81–85.

Danielson P. The effects of humidity on vacuum systems. R&D Magazine; 2001.

DeWitt D, Incropera F. Introduction to heat transfer. New York (NY): Wiley; 2002. 

Vol. 2, p. 52–72.

Fan L, Tai Y, Muller R. Integrated movable micromechanical structures for sensors 

and actuators. IEEE Trans Electron Devices. 1988;35(6):724–730.

Kim B, Jha C, White T, Candler R, Hopcroft M, Agarwal M, Park K, Melamud R, 

Chandorkar S, Kenny T. Temperature dependence of quality factor in MEMS 

resonators. In: Proceedings of the IEEE International Conference on Micro 

Electro Mechanical Systems (MEMS); 2006 Feb;17:590–593.

Kyocera. Material properties; n.d. [accessed 2015 Jul]. http://global.kyocera.com/ 

prdct/semicon/material/. 

Leland R. Mechanical-thermal noise in MEMS gyroscopes. IEEE Sensor J. 

2005;5(3).

Paquet A, Deshaies S, Desroches Y, Whalin J, Topart P. Influence of ceramic

package internal components on the performance of vacuum sealed uncooled 

bolometric detectors. Proc SPIE. 2013.

Permabond. Material safety data sheet. Pottstown (PA): Permabond; 2006.

Prikhodko I, Simon B, Sharma G, Zotov S, Trusov A, Shkel A. High and moderatelevel vacuum packaging of vibratory MEMS. Irvine (CA): University of 

California, Irvine; 2013.

Ramesham R, Evaluation of non-evaporable getters for high vacuum hermetic 

packages. Pasadena (CA): Jet Propulsion Laboratory, California Institute of 

Technology; 2004.

Santagata F, Iervolino E, Mele L, van Herwaarden A, Creemer J, Sarro P. An 

analytical model and verification for MEMS Pirani gauges. Delft 

(Netherlands): Delft University of Technology; 2011.

Spectrum Semiconductor Materials, Inc. SSM P/N LCC08423. San Jose, CA; n.d.
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35

Stanford Research Systems. Operating manual and programming reference: models 

RGA100, RGA200, and RGA300 Residual Gas Analyzer. Sunnyvale (CA): 

Stanford Research Systems; Rev 1.8; 2009.

Topalli E, Topalli K, Alper S, Serin T, Akin T. Pirani vacuum gauges using siliconon-glass and dissolved-wafer processes for the characterization of MEMS 

vacuum packaging. IEEE; 2009. 

Trusov A. Overview of MEMS gyroscopes: history, principles of operation, types 

of measurements. Irvine (CA): University of California, Irvine, CA; 2011.
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36

List of Symbols, Abbreviations, and Acronyms

ARL US Army Research Laboratory

COTS commercial off-the-shelf

Q-factor quality factor

DC direct current

GPS global positioning system

IMU inertial measurement unit

MEMS micro-electro-mechanical systems

PNT positioning, navigation, and timing

QMG quadruple-mass gyroscope

UAV unmanned aerial vehicle
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1 DEFENSE TECH INFO CTR

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P OLSON

2 RDECOM AMRDEC

(PDF) B GRANTHAM

T HUDSON

7 US ARMY RSRCH LAB

(PDF) RDRL SE K KAPPRA

RDRL SER L B PIEKARSKI

RDRL SER L G L SMITH

RDRL SER L J CONROY

RDRL SER L R KNIGHT

RDRL SER L R POLCAWICH 

RDRL SER P AMIRTHARAJ

1 UNAFFILIATED

(PDF) ANGELA MAIO
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