Abstract—This technology, moreover, the demand for new

Abstract—This paper aims to provide a review of
MEMS-Accelerometers (accs.) different operating principles. At first variety of
acceleration sensing and their basic principles as well as a brief overview of
their fabrication mechanism will be discussed and lastly the paper will be
focused on most commercialized and
well-known accelerometer technique, namely, capacitive.
Moreover, a comparison table of their performance based on acceleration sensor characteristics such as dynamic range, sensitivity,
resolution and linearity will be depicted. finally, an evaluation of the different sensing techniques of
MEMS-Accelerometer as well as the conclusion wraps-up the paper.

                                                                                                                                                    
I.         
Introduction

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Acceleration sensors are playing a vital
role in micromachined technology, moreover, the demand for new and high-performance accelerometers is increasing daily.
The first industry which took the benefits of MEMS-Accelerometers was the
automobile industry in 2000 by utilizing MEMS-Accs as for car suspension
systems and controllability and in the same way
for safety systems such as airbags system 1.
Nowadays the application scope of accelerometers covered almost every aspect of
engineering science. MEMS-Accs compare to conventional accelerometers have
advantages of extremely small size and ability to be mass produced and importantly
lower manufacturing costs 1.
Consequently, the application spectrum of these acceleration sensors is not
confined to car industry while they have opened up their way in multitude
branch of science. For instance, nowadays in aviation and aerospace industry and after the emerging the
modern technology autonomous unmanned aerial vehicles (UAVs) the demand for highly sensitive and low-cost accelerometers increased sharply 2. Moreover, MEMS accelerometers are now the crucial part of
space crafts and rockets navigation systems. Moreover, they are now an inseparable part of smart devices navigation
and tracking systems. Similarly, in Bio-engineering where the size of the sensor is highly under magnifier for
researchers, MEMS accelerometers are used for health monitoring with help of
implanting sensors inside the body 3. Based
on aforementioned applications different technology and principle has been used
up to now for their fabrication and operating method, the vast majority of application employed
capacitive and piezoresistive accelerometer
as their transduction mechanism and fabrication is easier to utilize, but there
are more different working principles which will be discussed in the next section
of this paper.

                                                                                                                                       
II.        
Operating
principles

As for every accelerometer,
the basic working principle is based on a fixed local inertial frame, beam, and
of course the proof mass. When an external forces apply the mass will be
displaced with respect to the local inertial frame,
the source of this force could be constant gravity force which is called static force or it could be caused by
shock or movement which can be named as dynamic forces 4. With reference to definition of sensor, acceleration sensor
should convert mechanical motion which has deflected the proof mass, into readable
computer signal, for this reason there are several transduction mechanisms
which some of them are more relevant such as Capacitive or Piezoresistive
accelerometers and also some other mechanisms like Optical, Piezoelectric, Thermal
and Tunneling, Piezoelectric, Electromagnetic, Surface Acoustic Wave (SAW) accelerometers.
Due to content restriction and less practical applications compare to other
mechanisms, in this paper all of the above-mentioned
principles except Electromagnetic and SAW will be discussed.

A.   
 Optical Accelerometers

The working principle of optical
accelerometers lies in characteristics of
a beam of light. compare to well-known capacitive based accelerometers,
optical-Accs exhibit better sensitivity and resolution as well as higher
thermal stability which make them
applicable in hazardous environments. Optical accelerometers instead of
measuring the displacement of proof mass
measure the variation of light wave characteristics like measuring the stress distribution
among the proof mass when it is deflected (Photoelastic
effect) or determining the effect of different forces and mass displacement on
optical signal phase (Phase modulation). Phase modulation is normally used when
the higher dynamic range is required. The
other methods are Intensity modulation which is simple for fabrication but
highly dependent on high-quality light
sources compare to Wavelength modulation which is completely independent of
light source deviation and is highly accurate and sensitive. The outstanding
advantage of Optical-Accs is their
immunity against electromagnetic interference(EMI) 5.

Figure. 1. Optical wavelength modulation based Accelerometer

 

The figure.1 shows the Wavelength modulation based Optical-Acc sensor by which
the light goes through the photonic crystal
(PhC) and then enter the photodetector
for measuring the acceleration, when an external forces applied to proof mass
it will move on its (y) axes which will cause a change
of output wavelength. Consequently, the magnitude and direction of acceleration
would be measured base on the wavelength difference occurred.

B.   
Thermal
Accelerometer

Thermal accelerometers compare to other
aforementioned techniques do not employ proof mass for sensing acceleration,
they utilize thermal convection phenomenon. Thermal-Accs generally consist of silicon etched SNx
heater with two temperature sensor on both sides
of it, inside the thermal isolated encapsulated
cavity. The heater reduces the density of its surrounded air(liquid) therefore when there is no acceleration two
temperature sensor will sense the same temperature figure.2(A). By applying
acceleration dense bubble will move within
the direction of applied acceleration which will cause an asymmetric
temperature profile for detectors figure.2(B), consequently, this temperature
difference will be detected and amplified for converting into a digital signal by the principle of Wheatstone bridge. 6

Figure 2 Heat Accs,(a) rest mode (b) acceleration applied

 

The fabrication
process of this accelerometer is simple which means lower manufacturing cost compared to other mechanisms.  Since there is no proof mass, the thermal accelerometer has extremely good shock resistance
and compare to capacitive sensors it has more sensitivity, on the other hand, the dynamic range is confined and low-frequency range makes it not suitable for instant shocks measurements or fall sensing. 6

C.   
Tunnel
Accelerometer

Tunneling-Accs typically consist of metal tip connected to a proof mass which has
few Nanometer distance to a counter electrode and the working principle lies in the quantum electron tunnelling. In order to activate the sensor small bias voltage
(around 100mV) is needed to be applied, this voltage consequently create a small current between the metal coated tip and
counter-electrode.  7

Figure 3 Simple Schematic of Tunnel Accelerometer

When an acceleration applied the movement of proof
mass will cause the sub-angstroms displacement of the tip which causes the change in tunnel current. The aim of this method is to keep the tunnel
current (1nA) constant over the time, therefore, feedback forces have applied to bring the mass back to its rest
position, as a result, the magnitude of acceleration could be measured by closed-loop detector circuit and with help of
variation of deflection voltage.  7

The design and
fabrication of Tunnel-Accs vary since the time they introduced, Cantilevered,
Lateral and Bulk-micromachined are some of them.
7 Tunneling accelerometers have low drive voltage supported by wide
frequency bandwidth as well as higher sensitivity compared to capacitive. On the other
hand, with reference to the Nanoscale gap,
they have complicated fabrication process and higher production costs.

D.  
Piezoelectric  Accelerometer

These kinds of accs.
take the benefit of the inherent piezoelectric effect
of materials. A piezoelectric acc. as shown in the figure.4 Usually, consists of a piezoelectric
material which is typically thin ZnO or PZT which is sandwiched by two
electrodes and deposited over silicon cantilever beam. 8

 

Figure 4 Principle schematic of the piezoelectric

 

         The beam is fixed to frame on one side
and on the other side there is proof mass. In
the presence of acceleration, mass displacement cause deformation of the beam, in the same
way, the piezo material experience compression or tensile. The
acceleration then could be measured by calculating the potential difference
occurred. PZT has higher piezoelectric
constant and sensitivity but it could not be integrated or miniaturized, On the
other hand, ZnO has lower sensitivity but
easy to integrate, additionally, new fabrication technology
compatibility and its sensitivity could be improved by miniaturization. Overall,
piezoelectric-Accs. Has high sensitivity and compare to capacitive, lower power
consumption and lower temperature dependence as well as higher bandwidth. 8

E.   
Piezoresistive
Accelerometer

The first MEMS
accelerometer was piezoresistive and was developed back in 19795. It took twenty years until the first
MEMS accelerometer commercialized in the market
by a car company for their safety systems. The backbone of this method is based
on resistivity variation of a material under the stress. Early designs of
piezoresistive-acc has a  beam that holds the proof mass and
supported by a fixed frame 9, moreover, piezo-resistors
were located on the special spot of the
beam where the maximum deformation and stress happens (usually edges) and the
readout circuit of them is based on Wheatstone bridge principle, figure.5(b).
acceleration and displacement of proof mass will cause beam deformation and consequently, the resistivity of piezo-resistors will change, resistance
variation will end up changes in the output voltage. piezoresistive accelerometers
are highly reliable and simple to fabricate but the integration is not simple.

Figure 5 three axes piezoresistive
accelerometer (a) model view (b) equivalent Wheatstone bridge model

 

Up to know almost
all of the papers are focused on improving the performance and sensitivity by
modifying the geometric design and sensing mechanism or by utilizing different
fabrication technologies. For instance, adding multiple beams instead of one flexure, figure.5(a) or using asymmetrically
gaped cantilever or ion etching the resistors on beam instead of thermal
diffusion.  In some papers, the lateral movement of mass has also
fabricated. Additionally, the length of flexure
also matters, the longer the flexure will cause, the lower resonant frequency
and therefore lower bandwidth. 9 Typically,
in order to protect the sensor from high G or instant shock, the upper and lower part of the sensor is covered by Glass in almost most of the fabrications.

F.   
Capacitive
Accelerometer

Capacitive-acc
is the among most famous accelerometers in
MEMS sensors, ADXL series is one the most successful accelerometers in
MEMS market. 10 Their working principle
is based on capacitance variation. The
proof mass is located in a way that has a narrow
gap with fix conductive electrodes, the displacement of the mass, therefore,
will cause a change in distance between mass and electrodes, therefore, the
capacitance will be varied. This variation then could be transferred to a digital signal with readout circuit. Capacitive-accs structures could be divided into lateral,
vertical or see-saw. 1 Lateral
accelerometers usually consist of surface micromachined
fix fingers as well as a mass which
shaped with sensing fingers, sensing in-plane acceleration in x-y axis, vertical
structures are usually bulk micromachined
and has bigger mass which is located between two fix electrodes, thus they have
better sensitivity and out of plane sensing in the z-axis. The see-saw accelerometers make use of torsional beams to
suspend the mass and making one side of structure heavier, hence, same as
verticals the have out of plane sensing mechanism. The outstanding advantages
of capacitive-accs are high sensitivity and DC response, simple and easy to
mass produce structure, high linearity and low power dissipation and easy to
integrate. The only drawback of capacitive accelerometers is that they are at
the mercy of electromagnetic interferences(EMI) which require special
packaging. Figure.6 Is an integrated 3-axis accelerometer with two in-plane
structure for x and z-axis and one out of
plane structure for z-axis which they connected to each other by polysilicon connectors. The fabrication of both of them is depicted in figure.7.

Figure 6 Three-axis single-chip micro-g accelerometer

 

1

N. Yazdi, F. Ayazi and K. Najafi, “Micromachined
Inertial Sensors,”

2

H. K. a. K. N. Junseok Chae, “An In-Plane
High-Sensitivity, Low-Noise Micro-g Silicon AccelerometerWith CMOS Readout
Circuitry,”  2004.

3

K. Imenes, “Implantable MEMS Acceleration Sensor for
Heart Monitoring Recent Development and Outlook,” HiVe – Vestfold
University College, Technology, Norway.

4

M. Andrejaši?c, “MEMS ACCELEROMETERS,” in University
of Ljubljana, 2008.

5

“A Proposal for an Optical MEMS Accelerometer Relied
on Wavelength Modulation With One Dimensional Photonic Crystal,” JOURNAL
OF LIGHTWAVE TECHNOLOGY, vol. 34, p. 22, 2016.

6

J. B. P. M. K. G. Rahul Mukherjee, “A review of
micromachined thermal accelerometers,” Journal of Micromechanics and
Microengineering, 2017.

7

X. G. P. Varun Kumar, “Single-Mask Field Emission
Based Tunable MEMS Tunneling Accelerometer,” in IEEE International
Conference on Nanotechnol, Rome, 2015.

8

J.-y. W. M.-h. X. H. G. Rui-Hua HAN, “DESIGN OF A
TRI-AXIAL MICRO PIEZOELECTRIC ACCELEROMETER,” in Symposium on
Piezoelectricity, Acoustic waves, and Device Applications, 2016.

9

A. L. R. Tarun Kanti Bhattacharyya, “MEMS
Piezoresistive Accelerometers,” in Micro and Smart Devices and
Systems, 2014.

10

S. T. A. Albarbar, “MEMS Accelerometers: Testing and
Practical Approach for Smart Sensing and Machinery Diagnostics,” Springer
International Publishing, vol. 2, 2017.

Figure 7 Fabrication process. (a) Boron doping; (b)
DRIE trench; (c) oxide,nitride, poly deposition; (d) pattern
oxide, nitride, poly; (e) electroplate metal;(f) anisotropic etching; (g) HF
release.

                                                                                                                                                    
III.       
Comparision

There are a variety of sensors in all of aforementioned
transduction mechanisms in different dynamic range (from micro-g ranged to
hundred kilos) and sensitivity as well as
DC response or linearity. Therefore, it is not an
easy task to compare this mechanism. For the sake of comparison six sensors
which have close dynamic range has been
selected and their performance has been written on
the table1.

 

 

Range

Sensitivity

Resolution

Non.lin

Optical

+  22

3.1816 nm g?1

n/a

Linear

Thermal

+10

375 mV/g

30 mg

Linear

Tunnel

-20-+10

133 mV/g

22.8 mg

0.6%

Piezo.res

50

3 mV/g

0.20 the mg

<1% Piezo.e + 25 0.21 mV/g 0.22 mg <2% Capaci. + 27 0.5 mV/g n/a Linear Table 1 MEMS Accelerometers Comparison Table                                                                                                                                                       IV.        Conclusion In this paper, six different transduction mechanism of the accelerometer, as well as their specifications with brief fabrication techniques descriptions, have been discussed. It worth to be noted that basically, each type of accelerometers has some pros and cons which make them applicable for the special and different application. For instance, EMI and temperature immunity of optical sensors for a special application which has electromagnetic fields or high sensitivity of Tunneling sensors for rocket navigation and good shock resistivity of Thermal sensors in high-g applications, simple fabrication of piezoresistive sensors for mass production and also low power consumption of piezoelectric sensors. The thing that makes the capacitive sensors different and put them in the first place in the market is that they have most of the above-mentioned advantages which make them applicable for wide variety spectrum of different applications.

Abstract—This paper aims to provide a review of
MEMS-Accelerometers (accs.) different operating principles. At first variety of
acceleration sensing and their basic principles as well as a brief overview of
their fabrication mechanism will be discussed and lastly the paper will be
focused on most commercialized and
well-known accelerometer technique, namely, capacitive.
Moreover, a comparison table of their performance based on acceleration sensor characteristics such as dynamic range, sensitivity,
resolution and linearity will be depicted. finally, an evaluation of the different sensing techniques of
MEMS-Accelerometer as well as the conclusion wraps-up the paper.

                                                                                                                                                    
I.         
Introduction

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Acceleration sensors are playing a vital
role in micromachined technology, moreover, the demand for new and high-performance accelerometers is increasing daily.
The first industry which took the benefits of MEMS-Accelerometers was the
automobile industry in 2000 by utilizing MEMS-Accs as for car suspension
systems and controllability and in the same way
for safety systems such as airbags system 1.
Nowadays the application scope of accelerometers covered almost every aspect of
engineering science. MEMS-Accs compare to conventional accelerometers have
advantages of extremely small size and ability to be mass produced and importantly
lower manufacturing costs 1.
Consequently, the application spectrum of these acceleration sensors is not
confined to car industry while they have opened up their way in multitude
branch of science. For instance, nowadays in aviation and aerospace industry and after the emerging the
modern technology autonomous unmanned aerial vehicles (UAVs) the demand for highly sensitive and low-cost accelerometers increased sharply 2. Moreover, MEMS accelerometers are now the crucial part of
space crafts and rockets navigation systems. Moreover, they are now an inseparable part of smart devices navigation
and tracking systems. Similarly, in Bio-engineering where the size of the sensor is highly under magnifier for
researchers, MEMS accelerometers are used for health monitoring with help of
implanting sensors inside the body 3. Based
on aforementioned applications different technology and principle has been used
up to now for their fabrication and operating method, the vast majority of application employed
capacitive and piezoresistive accelerometer
as their transduction mechanism and fabrication is easier to utilize, but there
are more different working principles which will be discussed in the next section
of this paper.

                                                                                                                                       
II.        
Operating
principles

As for every accelerometer,
the basic working principle is based on a fixed local inertial frame, beam, and
of course the proof mass. When an external forces apply the mass will be
displaced with respect to the local inertial frame,
the source of this force could be constant gravity force which is called static force or it could be caused by
shock or movement which can be named as dynamic forces 4. With reference to definition of sensor, acceleration sensor
should convert mechanical motion which has deflected the proof mass, into readable
computer signal, for this reason there are several transduction mechanisms
which some of them are more relevant such as Capacitive or Piezoresistive
accelerometers and also some other mechanisms like Optical, Piezoelectric, Thermal
and Tunneling, Piezoelectric, Electromagnetic, Surface Acoustic Wave (SAW) accelerometers.
Due to content restriction and less practical applications compare to other
mechanisms, in this paper all of the above-mentioned
principles except Electromagnetic and SAW will be discussed.

A.   
 Optical Accelerometers

The working principle of optical
accelerometers lies in characteristics of
a beam of light. compare to well-known capacitive based accelerometers,
optical-Accs exhibit better sensitivity and resolution as well as higher
thermal stability which make them
applicable in hazardous environments. Optical accelerometers instead of
measuring the displacement of proof mass
measure the variation of light wave characteristics like measuring the stress distribution
among the proof mass when it is deflected (Photoelastic
effect) or determining the effect of different forces and mass displacement on
optical signal phase (Phase modulation). Phase modulation is normally used when
the higher dynamic range is required. The
other methods are Intensity modulation which is simple for fabrication but
highly dependent on high-quality light
sources compare to Wavelength modulation which is completely independent of
light source deviation and is highly accurate and sensitive. The outstanding
advantage of Optical-Accs is their
immunity against electromagnetic interference(EMI) 5.

Figure. 1. Optical wavelength modulation based Accelerometer

 

The figure.1 shows the Wavelength modulation based Optical-Acc sensor by which
the light goes through the photonic crystal
(PhC) and then enter the photodetector
for measuring the acceleration, when an external forces applied to proof mass
it will move on its (y) axes which will cause a change
of output wavelength. Consequently, the magnitude and direction of acceleration
would be measured base on the wavelength difference occurred.

B.   
Thermal
Accelerometer

Thermal accelerometers compare to other
aforementioned techniques do not employ proof mass for sensing acceleration,
they utilize thermal convection phenomenon. Thermal-Accs generally consist of silicon etched SNx
heater with two temperature sensor on both sides
of it, inside the thermal isolated encapsulated
cavity. The heater reduces the density of its surrounded air(liquid) therefore when there is no acceleration two
temperature sensor will sense the same temperature figure.2(A). By applying
acceleration dense bubble will move within
the direction of applied acceleration which will cause an asymmetric
temperature profile for detectors figure.2(B), consequently, this temperature
difference will be detected and amplified for converting into a digital signal by the principle of Wheatstone bridge. 6

Figure 2 Heat Accs,(a) rest mode (b) acceleration applied

 

The fabrication
process of this accelerometer is simple which means lower manufacturing cost compared to other mechanisms.  Since there is no proof mass, the thermal accelerometer has extremely good shock resistance
and compare to capacitive sensors it has more sensitivity, on the other hand, the dynamic range is confined and low-frequency range makes it not suitable for instant shocks measurements or fall sensing. 6

C.   
Tunnel
Accelerometer

Tunneling-Accs typically consist of metal tip connected to a proof mass which has
few Nanometer distance to a counter electrode and the working principle lies in the quantum electron tunnelling. In order to activate the sensor small bias voltage
(around 100mV) is needed to be applied, this voltage consequently create a small current between the metal coated tip and
counter-electrode.  7

Figure 3 Simple Schematic of Tunnel Accelerometer

When an acceleration applied the movement of proof
mass will cause the sub-angstroms displacement of the tip which causes the change in tunnel current. The aim of this method is to keep the tunnel
current (1nA) constant over the time, therefore, feedback forces have applied to bring the mass back to its rest
position, as a result, the magnitude of acceleration could be measured by closed-loop detector circuit and with help of
variation of deflection voltage.  7

The design and
fabrication of Tunnel-Accs vary since the time they introduced, Cantilevered,
Lateral and Bulk-micromachined are some of them.
7 Tunneling accelerometers have low drive voltage supported by wide
frequency bandwidth as well as higher sensitivity compared to capacitive. On the other
hand, with reference to the Nanoscale gap,
they have complicated fabrication process and higher production costs.

D.  
Piezoelectric  Accelerometer

These kinds of accs.
take the benefit of the inherent piezoelectric effect
of materials. A piezoelectric acc. as shown in the figure.4 Usually, consists of a piezoelectric
material which is typically thin ZnO or PZT which is sandwiched by two
electrodes and deposited over silicon cantilever beam. 8

 

Figure 4 Principle schematic of the piezoelectric

 

         The beam is fixed to frame on one side
and on the other side there is proof mass. In
the presence of acceleration, mass displacement cause deformation of the beam, in the same
way, the piezo material experience compression or tensile. The
acceleration then could be measured by calculating the potential difference
occurred. PZT has higher piezoelectric
constant and sensitivity but it could not be integrated or miniaturized, On the
other hand, ZnO has lower sensitivity but
easy to integrate, additionally, new fabrication technology
compatibility and its sensitivity could be improved by miniaturization. Overall,
piezoelectric-Accs. Has high sensitivity and compare to capacitive, lower power
consumption and lower temperature dependence as well as higher bandwidth. 8

E.   
Piezoresistive
Accelerometer

The first MEMS
accelerometer was piezoresistive and was developed back in 19795. It took twenty years until the first
MEMS accelerometer commercialized in the market
by a car company for their safety systems. The backbone of this method is based
on resistivity variation of a material under the stress. Early designs of
piezoresistive-acc has a  beam that holds the proof mass and
supported by a fixed frame 9, moreover, piezo-resistors
were located on the special spot of the
beam where the maximum deformation and stress happens (usually edges) and the
readout circuit of them is based on Wheatstone bridge principle, figure.5(b).
acceleration and displacement of proof mass will cause beam deformation and consequently, the resistivity of piezo-resistors will change, resistance
variation will end up changes in the output voltage. piezoresistive accelerometers
are highly reliable and simple to fabricate but the integration is not simple.

Figure 5 three axes piezoresistive
accelerometer (a) model view (b) equivalent Wheatstone bridge model

 

Up to know almost
all of the papers are focused on improving the performance and sensitivity by
modifying the geometric design and sensing mechanism or by utilizing different
fabrication technologies. For instance, adding multiple beams instead of one flexure, figure.5(a) or using asymmetrically
gaped cantilever or ion etching the resistors on beam instead of thermal
diffusion.  In some papers, the lateral movement of mass has also
fabricated. Additionally, the length of flexure
also matters, the longer the flexure will cause, the lower resonant frequency
and therefore lower bandwidth. 9 Typically,
in order to protect the sensor from high G or instant shock, the upper and lower part of the sensor is covered by Glass in almost most of the fabrications.

F.   
Capacitive
Accelerometer

Capacitive-acc
is the among most famous accelerometers in
MEMS sensors, ADXL series is one the most successful accelerometers in
MEMS market. 10 Their working principle
is based on capacitance variation. The
proof mass is located in a way that has a narrow
gap with fix conductive electrodes, the displacement of the mass, therefore,
will cause a change in distance between mass and electrodes, therefore, the
capacitance will be varied. This variation then could be transferred to a digital signal with readout circuit. Capacitive-accs structures could be divided into lateral,
vertical or see-saw. 1 Lateral
accelerometers usually consist of surface micromachined
fix fingers as well as a mass which
shaped with sensing fingers, sensing in-plane acceleration in x-y axis, vertical
structures are usually bulk micromachined
and has bigger mass which is located between two fix electrodes, thus they have
better sensitivity and out of plane sensing in the z-axis. The see-saw accelerometers make use of torsional beams to
suspend the mass and making one side of structure heavier, hence, same as
verticals the have out of plane sensing mechanism. The outstanding advantages
of capacitive-accs are high sensitivity and DC response, simple and easy to
mass produce structure, high linearity and low power dissipation and easy to
integrate. The only drawback of capacitive accelerometers is that they are at
the mercy of electromagnetic interferences(EMI) which require special
packaging. Figure.6 Is an integrated 3-axis accelerometer with two in-plane
structure for x and z-axis and one out of
plane structure for z-axis which they connected to each other by polysilicon connectors. The fabrication of both of them is depicted in figure.7.

Figure 6 Three-axis single-chip micro-g accelerometer

 

1

N. Yazdi, F. Ayazi and K. Najafi, “Micromachined
Inertial Sensors,”

2

H. K. a. K. N. Junseok Chae, “An In-Plane
High-Sensitivity, Low-Noise Micro-g Silicon AccelerometerWith CMOS Readout
Circuitry,”  2004.

3

K. Imenes, “Implantable MEMS Acceleration Sensor for
Heart Monitoring Recent Development and Outlook,” HiVe – Vestfold
University College, Technology, Norway.

4

M. Andrejaši?c, “MEMS ACCELEROMETERS,” in University
of Ljubljana, 2008.

5

“A Proposal for an Optical MEMS Accelerometer Relied
on Wavelength Modulation With One Dimensional Photonic Crystal,” JOURNAL
OF LIGHTWAVE TECHNOLOGY, vol. 34, p. 22, 2016.

6

J. B. P. M. K. G. Rahul Mukherjee, “A review of
micromachined thermal accelerometers,” Journal of Micromechanics and
Microengineering, 2017.

7

X. G. P. Varun Kumar, “Single-Mask Field Emission
Based Tunable MEMS Tunneling Accelerometer,” in IEEE International
Conference on Nanotechnol, Rome, 2015.

8

J.-y. W. M.-h. X. H. G. Rui-Hua HAN, “DESIGN OF A
TRI-AXIAL MICRO PIEZOELECTRIC ACCELEROMETER,” in Symposium on
Piezoelectricity, Acoustic waves, and Device Applications, 2016.

9

A. L. R. Tarun Kanti Bhattacharyya, “MEMS
Piezoresistive Accelerometers,” in Micro and Smart Devices and
Systems, 2014.

10

S. T. A. Albarbar, “MEMS Accelerometers: Testing and
Practical Approach for Smart Sensing and Machinery Diagnostics,” Springer
International Publishing, vol. 2, 2017.

Figure 7 Fabrication process. (a) Boron doping; (b)
DRIE trench; (c) oxide,nitride, poly deposition; (d) pattern
oxide, nitride, poly; (e) electroplate metal;(f) anisotropic etching; (g) HF
release.

                                                                                                                                                    
III.       
Comparision

There are a variety of sensors in all of aforementioned
transduction mechanisms in different dynamic range (from micro-g ranged to
hundred kilos) and sensitivity as well as
DC response or linearity. Therefore, it is not an
easy task to compare this mechanism. For the sake of comparison six sensors
which have close dynamic range has been
selected and their performance has been written on
the table1.

 

 

Range

Sensitivity

Resolution

Non.lin

Optical

+  22

3.1816 nm g?1

n/a

Linear

Thermal

+10

375 mV/g

30 mg

Linear

Tunnel

-20-+10

133 mV/g

22.8 mg

0.6%

Piezo.res

50

3 mV/g

0.20 the mg

<1% Piezo.e + 25 0.21 mV/g 0.22 mg <2% Capaci. + 27 0.5 mV/g n/a Linear Table 1 MEMS Accelerometers Comparison Table                                                                                                                                                       IV.        Conclusion In this paper, six different transduction mechanism of the accelerometer, as well as their specifications with brief fabrication techniques descriptions, have been discussed. It worth to be noted that basically, each type of accelerometers has some pros and cons which make them applicable for the special and different application. For instance, EMI and temperature immunity of optical sensors for a special application which has electromagnetic fields or high sensitivity of Tunneling sensors for rocket navigation and good shock resistivity of Thermal sensors in high-g applications, simple fabrication of piezoresistive sensors for mass production and also low power consumption of piezoelectric sensors. The thing that makes the capacitive sensors different and put them in the first place in the market is that they have most of the above-mentioned advantages which make them applicable for wide variety spectrum of different applications.

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