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MEMS In Smart Phone
Transcript of MEMS In Smart Phone
Smart phones have many MEMS sensors inside them
including, accelerometers, microphones, cameras,
gyroscopes, temperature, humidity, magnetic field
sensors and more.
The problem becomes more acute as image sensor resolution increases, pixel
dimensions decrease, and f-number decreases.
VCMs are challenged to serve the demand for thinner handsets with better image
quality. Making a VCM smaller requires smaller coils, magnets and springs.
Because magnetic force is proportional to volume, smaller coils and magnets require
more current to create enough force for actuation, making the power consumption
and heat problems worse. Furthermore, smaller springs are weaker, exacerbating
hysteresis of stroke, lens tilt, reliability, and de-centering issues.
VCM technology is over 100 years old. This means that there are limited
opportunities for further cost reduction, thus providing a commercial opportunity for a
competing technology that can deliver better performance at a suitable cost
Accelerometer Output Under Gravity and Acceleration
Changes in orientation are described by rotations in roll φ, pitch θ and yaw ψ about the x, y and z axes
Calculating the Tilt Angle
Selecting Portrait and Landscape Modes
The solution is a simple state machine in which the accelerometer reading leads to transitions between the
screen orientations rather than directly defining the screen orientation. Simple state transition rules are
• (|Gpz| < 0.5g) AND (Gpx > 0.5g) AND (|Gpy| < 0.4g): Change orientation to Top
• (|Gpz| < 0.5g) AND (Gpx < -0.5g) AND (|Gpy| < 0.4g): Change orientation to Bottom
• (|Gpz| < 0.5g) AND (Gpy > 0.5g) AND (|Gpx| < 0.4g): Change orientation to Right
• (|Gpz| < 0.5g) AND (Gpy < -0.5g) AND (|Gpx| < 0.4g): Change orientation to Left.
RESISTIVE TOUCH SCREENS
Resistive touch screen systems are the most common type of
touch screen technology in today’s market. These devices
are used in many applications, such as cell phones, handheld
games, GPS navigation devices, and even some digital
The resistive touch screen technology operates in a
very simple way. These screens are built using two layers of
the conductive material Indium Tin Oxide (ITO), separated by a small gap of air . The bottom layer is generally on glass, and the top on a flexible material, often plastic . When the user presses down on the top ITO layer, it physically bends to make contact with the bottom ITO layer, changing the resistance of the two layers . A typical resistive touch screen uses 4 wires, 2 of them on each panel. As seen in Figure 3, each panel corresponds to a different axis. These perpendicular axes allow the computer to take the measurements of the change in resistance from each panel, and calculate the position of the touch point from its X and Y components .
CAPACITIVE TOUCH SCREENS
Capacitive touch screens are very important within the field of touch screen technology. In the early 1990s, this technology made its initial appearance into the touch screen market in laptop computers, as touch pads . Recently, capacitive popularity has grown, as it has become one of the leading technologies used in touch screen devices. In 2001, it began appearing in consumer devices, such as MP3-players and smart phones . This increase in attention is likely due to the effectiveness of its design, its use of multi-touch technology, and the popularity of Apple products using this technology: iPod Touch, iPhone and most recently the iPad.
The design of projected capacitive touch screens is
somewhat similar to that of resistive touch screens, in that
they both utilize 2 layers of ITO, with perpendicular
conductive measuring strips on the ends of each layer,
which are encased between two glass layers (See Figure 4).
This “grid,” formed by the perpendicular conductive layers,
projects the electric field through the top layer of glass-
hence the name projected capacitive touch screens
Because of this projection, when the user touches the top layer of glass it “changes the measured
capacitance values of the electrodes closest to it” .
This change in capacitance is due to the slight electromagnetic charge contained in the
human body . These changes in capacitance are measured and calculated as touch points in a very similar way to resistive touch screens, by using the X and Y components.
Projected Capacitive Touch Screens
Surface Capacitive Touch Screens
Surface capacitive is another form of capacitive touch screen technology.
The primary difference between surface capacitive and projected capacitive is that surface capacitive uses only one ITO surface .
This layer calculates touch points using principles that are very similar to projected capacitive touch screens, in that touch points are observed
by changes in capacitance if the ITO layer in the touch screen. However, these touch points are measured in a very different way.
The computer measures the change in
capacitance from each corner of the ITO layer, and with
these 4 separate measurements, the X and Y coordinates of
the touch point are calculated
An important feature of capacitive touch screens is their ability to recognize and calculate multiple touch points at one time, commonly called multi-touch. “Multi-touch technology has been around since early research at the University of Toronto in 1982” . The uses of this technology are very vast, allowing for greater human-computer interaction. This technology is traditionally associated with capacitive touch screens, but is not limited to this technology. It can also be found in infrared touch screens and is beginning to appear in resistive touch screens . Currently, multi-touch technology is being used with a purpose similar to the function keys (Control, Alt, Option, Command, etc.) on a standard keyboard. By adopting these functions, the user is able to complete the same tasks as before, but with one hand. With advances in hardware, multi touch will allow multiple users to access the same device simultaneously,
An important feature of capacitive touch screens is their ability to recognize and calculate multiple touch points at one time
What is Touch Screen?
An electronic visual display that locates the coordinates of a users touch within display area
Works independently of what is being displayed on screen
Touch Screen Technology
Four different technologies used to make touch screens today:
Surface Acoustic Wave (SAW)
Infrared LED or Optical
Surface Acoustic Wave Touch Screens
Surface consists of glass overlay with transmitting and receiving transducers
Electrical signals sent to the transmitting transducers converts to ultrasonic waves
Waves are directed across screen by reflectors then directed to receiving transducers
When finger touches screen it absorbs waves
Received values are compared to stored digital maps to calculate x and y coordinates
Best optical quality
High surface durability and seal
Activated by multiple sources
Contaminates on screen can cause false-touches
Infrared/Optical Touch Screens
Uses infrared LEDs and matching photodetectors
Touching screen interrupts LEDs
Cameras detect reflected LED caused by touch
Controller able to calculate coordinates from camera data
High optical clarity
Can scale to large sizes
Cameras can get out of alignment
In order to discuss MEMS
gyroscopes we must first understand
gyroscopes in general and what role they
play in science. Technically, a
gyroscope is any device that can
measure angular velocity.
Traditional Gyroscope Function
Gyroscopes function differently
depending on their type. Traditional
spinning gyroscopes work on the basis
that a spinning object that is tilted
perpendicularly to the direction of the
spin will have a precession. The
precession keeps the device oriented in a
vertical direction so the angle relative to
the reference surface can be measured.
1- Optical Gyroscopes
2- Draper Tuning Fork Gyro
3- Piezoelectric Gyroscopes
How does it work?
If an object is moving along one axis, and it is rotated above another, it will feel a Coriolis force in the third axial direction
A gyroscope will have a mass oscillating back and force along the first axis, and plates on either side of the mass in the third direction (direction of the Coriolis force)
When a rotating is detected around the second direction, the capacitance changes
Laser Ring Gyro
Optical gyroscopes are most commonly
ring laser gyroscopes. A
laser source outputs two beams traveling
in an opposite direction around the ring
until they reach the detector. The
detector counts the beat frequency of the
combined light wave. This beat
frequency is directly proportional to the
angle of rotation of the gyroscope.
Optical gyroscopes are a great
improvement to the spinning mass
gyroscopes because there is no wear,
greater reliability and smaller size and
Draper Tuning Fork Gyro
One of the most widely used
micro-machined gyroscopes is the tuning
The design consists
of two tines connected to a junction bar
which resonate at certain amplitude.
When the tines rotate, Coriolis force
causes a force perpendicular to the tines
of the fork. The force is then detected as
bending of the tuning fork or a torsional
force These forces are
proportional to the applied angular rate,
from which the displacements can be measured in a capacitive fashion.
Electrostatic, electromagnetic, or
piezoelectric mechanisms can be used to
detect the force.
Piezoelectric plate with vibrating thickness
When the vibrating plate is
rotated about an axis perpendicular to
the drive voltage, a voltage is produced
in the third perpendicular direction. This
output voltage is proportional to the
Coriolis effect causes a voltage form the material
Very simple design and geometry
Lower input voltage than vibrating mass
Measures rotation in two directions with a single device
Adjusting orientation electronically is possible
Output is large when Ω = 0
The incumbent actuator technology for miniature AF cameras is the voice coil motor.
VCMs are named as such because they are based on the principles of attraction and
repulsion between magnets to generate sound from electricity (see Fig.). The
technology was first patented in 1874.
The Voice Coil Motor
Operation of a VCM involves passing current through the electromagnet (coil). This
creates a magnetic field that is repulsive with respect to the permanent magnets,
causing the lens holder to move vertically away from the image sensor. The restoring force is provided by springs. The rest position is infinity focus
Silicon MEMS technology is able to integrate all three parts of a linear actuator into a
single component. As shown in Fig. 2, these are a stage, to provide vertical movement,
a spring to provide the restoring force, and an electrostatic comb drive to displace the
Using MEMS, the movement of the stage can be precisely controlled. This makes it
possible to employ a novel optical configuration where only the first lens is moved, while
the remainder of the lens module is locked in an optimal position. Using this approach,
excellent image quality is obtained over the entire focus range from 10 cm to infinity,
and a number of other important benefits also result.
There are several reasons for the dramatic speed advantage offered by mems|cam:
1) Fast settling time: The mems|cam moves a single lens weighing a mere 3.5 mg,
but a VCM must move the entire lens module holder, weighing about 45 mg. VCMs
must also travel farther, approximately 250 µm from infinity to macro, compared to
just 80 µm for MEMS. The silicon MEMS comb drive system has inherently less
oscillation, typically <10 ms, compared to the metal springs and magnets of VCM.
2) Less hysteresis: mems|cam modules can also execute autofocus algorithms faster
than VCM-based cameras due to improved positional accuracy and lack of
hysteresis. The MEMS AF actuator is extremely accurate, with <1 µm of directional
hysteresis. A VCM is far less predictable in its location due to directional hysteresis
(typically about 10-20 µm), temperature dependencies, and coil resistance variation.
This necessitates open-loop control with multiple adjustments before the focus is
Characteristics of MEMS AF Cameras
DOC’s mems|cam integrates a MEMS actuator and novel optics
Lower Power Consumption and Cooler Operation
Smaller Z-Height and XY-Footprint
Better Reliability and Longer Lifetime
Fast settling time
Simple, Scalable, Solid-State Construction
The MEMS Revolution in Smartphones
Used to figure out where
How do they work?
A receiver will receive multiple signals from different
satellites at different times, depending on the distance to each satellite
• When it receives a transmission, based on the time it takes to get the packet it can determine how far it is from the satellite
• It must be on a sphere centered at where the satellite is, with a radius of the distance it just computed
• Once you have several spheres, the receiver lies at the intersection of those spheres
Measure the absolute and relative Humidity
Measurement of temperature is critical in modern electronic devices, especially
laptop computers and other portable devices with densely packed circuits, which dissipate
considerable power in the form of heat. Knowledge of system temperature can also be
used to effectively control battery charging as well as prevent damage to microprocessor.
Compact high power portable equipment often has fan cooling to maintain junction temperature at proper levels.
1.1) portable equipment,
1.2) CPU temperature,
1.3) battery temperature,
2.1) battery charging,
2.2) process control
What is a sensor?
A converter that measures a physical quantity and converts it into a signal which can be read by an observer or by an instrument …
Sensors have been used in cellphones since they were invented …
Microphone, number keys
What made smartphones smart?
Traditional autofocus camera modules employ voice coil
motors to move the lens module along the optical axis of
the camera. This technology – originally patented in 1874 –
has reached a point of diminishing returns, where
further reduction in size or cost creates unacceptable
Mechanical actuators based on silicon MEMS have
fundamentally different mechanical and electrical
characteristics, as well as the advantage of modern
manufacturing processes. This makes them highly suitable
for next-generation miniature autofocus cameras, providing
greater autofocus speed, dramatically reduced power
consumption, and higher precision
VCMs suffer from hysteresis
VCMs suffer from lens tilt and de-centering
VCM technology is over 100 years old
VCMs consume excessive power
A comb drive is a pair of electrically conductive structures arranged so the interdigitated
fingers never touch. When a DC voltage is applied, the resulting electrostatic charge
develops an attractive force that causes the combs to be drawn together. By attaching
a lens in the center, a silicon MEMS autofocus actuator (Fig. 3) can be created.
Anisotropic magnetoresistance (AMR)
is another approach that was introduced
a few years ago. This concept
makes use of a common material, permalloy,
to act as a magnetometer. Permalloy
is an alloy containing roughly
80% nickel and 20% iron. The alloy’s
resistance depends on the angle between
the metallization and the direction
of current flow. In a magnetic
field, magnetization rotates toward
the direction of the magnetic field and
the rotation angle depends on the external