What are Acoustic Wave (SAW) Applications?

university wafer substrates

Wafers for Acoustic Wave (SAW) Devices

A researcher at a large US university requested the following:

We are working on the multilayer Surface acoustic wave (SAW) devices. Towards that we want to deposit thin film (1 to 5 microns) Aluminum nitride (AlN) on Si or SiC or any other substrate which can sustain temperature up to 500 Celsius, the substrate option is discussable. We aim to utilize piezoelectric properties of AlN, by depositing interdigital transduces (IDTs) on top of that. The options are discussable later. May you please let us know If you have such facility to address our requirements?

 

UniversityWafer, Inc. Replied

We can help you fabricate your acoustic wave device!

Based on your requirements,We can deposit thin film (1 to 5 microns) Aluminum nitride (AlN) on Silicon, SiC and Sapphire Substrate wafer,the wafer size available from 2'' to 8'',all these can sustain temperature up to 500 Celsius

  1. Thin film 2 microns  Aluminum nitride (AlN) on 350um thick Double sides polished High Purity Semi insulating SiC substrate wafer
  2. Thin film 2 microns  Aluminum nitride (AlN) on 430um thick Single side polished C-plane<0001> Sapphire substrate wafer

Reference #265045 for specs and pricing

Get Your Quote FAST!

What are Some Acoustic Wave (SAW) Devices?

Surface Acoustic Wave (SAW) cavities are among the best-known acoustic devices in the application of chemical sensing. Surface acoustic wave (SAW) devices are used extensively in various fields, and they will remain very important for the foreseeable future. Surface acoustic wave (SAW) devices are recognized for their versatility and effectiveness for controlling and processing electric signals. Surface Acoustic Wave Sensors utilize digital-to-interactive converters to produce physical waves and convert them back into an electrical signal.

Below are just some acoustic wave devices:

  • wavemode transducers
  • uv detection
  • wave sensors 
  • multilayer sensor
  • wavemode converter
  • surface acoustic
  • attractive piezoelectric
  • pulse lasers
  • saw transducers
  • detection performance
  • acoustic stimulation 
  • acoustic method
  • uv absorption 
  • acoustic surface
  • wave propagation    

Recently, another type of transducer with alternative wave modes, surface acoustic waves (SAWs), has been investigated for neuromodulation. In comparison, Surface Acoustic Wave (SAW) devices, which are producing wavemodes that are increasingly being applied to biomedical devices, produce less self-heating, are smaller, and generate less cavitation. Although the local heat rejection cannot be controlled, a SAW device for a given power may produce less self-heating than a bulk wavemode converter, because SAW energy is contained in the material surface. Because both bulk-wavemode transducers and SAW transducers produce an acoustic field by electrically exciting the piezoelectric material, and both cases produce sinusoidal stress wavefronts that are experienced by the tissues, it is expected that the SAW devices will modulate neural activity by a similar mechanism.

Video: Acoustic Wave Technology for Industries

Acoustic Wave (SAW) Applications

An acoustic wave device is a sensor that uses sound waves to detect a variety of physical stimuli and phenomena. They can detect torque, force, shock, and more. Here are some examples of acoustic wave applications. Read on to learn more about the technology and applications that make acoustic wave devices so useful in everyday life. Also, find out how these sensors are used in real-time monitoring and control.

Surface Acoustic Wave (SAW) Devices are Widely used in Electronic Systems

The acoustic waves generated by surface acoustic wave resonators (SAWs) have a wide frequency range and are suitable for chemical sensing. The devices are capable of recording even small changes in frequency due to a small mass loading. These devices are compact, thermally stable, and can be combined with host-guest interactions, metal oxide coatings, functional polymers, and biological receptors.

The basic design of a surface acoustic wave device consists of two sets of metallic interdigital transducers deposited on a piezoelectric material. The interdigital transducer, or IDT, generates an acoustic wave across the crystal surface. The wave's frequency is determined by the width of its interdigital transducer.

The SAWs have a higher velocity than their bulk counterparts. This allows them to be used in communication systems and other electronic systems. They can be used to filter signals and detect their phase. The SAWs also serve as an excellent source of energy for circuits, including DC to DC converters. These devices are used in the following ways:

Piezoelectric materials can be easily processed. Many common materials are inexpensive and thermally stable. However, they are not suitable for aqueous phase operation. The TFC values and the cutting angle structure of piezoelectric materials vary greatly. Generally, quartz, lithium niobate, and aluminum nitride are the most stable. The last two types of materials have a higher SAW velocity than their counterparts.

The SAW device can be made of a piezoelectric material or a silicon semiconductor. It can be manufactured using conventional silicon-MEMS processing technologies. A chemical recognition layer is usually deposited between two sets of IDTs. This layer can be either an output electrode or an input electrode. If the IDTs are bonded together, they can form a two-port device.

What are Acoustic Wave (SAW) Sensors?

Acoustic wave sensors are extremely versatile, intrinsically reliable, rugged, and cheap. These sensors can be passively or wirelessly interrogated. This is an advantage if the sensor must monitor a moving object. Acoustic wave sensors can also measure various physical properties, including force, acceleration, and viscosity. In addition, they do not require any power supply or external antenna. Listed below are some of the common applications of acoustic wave sensors.

Piezoelectric materials are a common component in acoustic wave devices. Piezoelectricity is a phenomenon discovered by the Curie brothers and Wilhelm Hankel in 1881. It was a curiosity until 1921, when Walter Cady used a quartz resonator to stabilize electronic oscillators. Piezoelectricity is the production of electrical charges by the imposition of mechanical stress on a material. Acoustic wave sensors use this property to generate an electrical signal in the presence of a mechanical wave.

There are three types of acoustic wave devices: the flexural plate wave, the shear-horizontal acoustic plate mode sensor, and the Love wave. The latter is used to detect shock. The latter is also used in surface-skimming bulk waves. A third type of acoustic wave sensor uses waves traveling between the top and bottom surfaces. The flexural plate wave is the most common form of acoustic waves.

Moreover, acoustic waves have the ability to manipulate matter in a variety of systems. Microfluidics applications have benefited from the application of acoustics in microfluidics, spawning new technologies. Acoustic systems can be used for varying modes of manipulation, ranging from single cells to large modal animal models. They can also be used in nanoparticle patterning.

Acoustic Waves are Sensitive to Perturbations

The application of a strain can change the equation of motion for acoustic waves. These changes depend on the initial stress, material elastic constants, and density. These parameters were changed and different strains were introduced to the original equation. The resulting acoustic velocity was then measured at different frequencies. The result was compared to the measured value to determine the effect of a different guided layer.

There are two types of boundary conditions for acoustic waves: radiation and port conditions. Port conditions are important for numerical applications because they help model the effect of acoustic waves. A waveguide inlet should allow waves to pass through, while the outlet should allow reflected waves to escape. In the case of a nonlinear system, the boundary conditions must fulfill the Sommerfeld radiation condition, which states that waves propagate toward infinity.

A two-layer device with a liquid layer is more sensitive than one. The second guided layer can be optimized based on the properties of the liquid layer. Acoustic wave sensors are sensitive to perturbations in liquid layers. By understanding the relationship between the properties of the liquid layer and the sensitivity of a sensor, these devices may be able to detect analytes and biological samples in liquid. This research is ongoing, but a four-layer system has already been used for several applications.

The commercially available acoustic wave devices have many physical parameters that must be taken into consideration. In the telecommunications industry, acoustic wave devices must be hermetically sealed to prevent leakage and detect acoustic disturbances. The presence of any disturbance will cause unwanted changes in the sensor's output. The displacement of the SH-SAW sensor is parallel to the device's surface.

Acoustic Waves Create Less Cavitation

The acoustic cavitation phenomenon occurs when high-power acoustic waves induce micron and submicron-sized bubbles in a fluid. The acoustic wave pressure amplitude exceeds a threshold at which cavitation nuclei form. Pressure amplitudes below 1000 bars peak negative correspond to atomic or molecular-sized cavities in liquid bulk. For smaller cavitation nuclei, stronger tensile pressures are required.

The high surface tension of the bubble in the path of an acoustic wave causes the bubble to expand. The implosive collapse releases mechanical energy concentrated in the bubble. Bubbles growing to about two-and-a-half times their equilibrium size will explode at supersonic speeds, leading to a catastrophic explosion. The phenomenon is also called transient or inertial cavitation. These properties may explain the energetic manifestations of cavitation. In some applications, such as surface erosion and particle eviction, cavitation is beneficial.

Acoustic wave applications tend to create less cavitation when the pressure is lower. This is because the smaller bubble size seeds the cavitation process. This reduces the intensity of energy release. However, transient cavitation is preferred because of its lower intensity. However, transient cavitation is not without its drawbacks. It's essential to understand how cavitation works before implementing an acoustic wave application.

SAW devices operate at frequencies of 10 to 100 MHz, higher than the lowest frequencies of bulk ultrasonic resonators. Their high frequency counterparts don't create the high frequency acoustic waves necessary to induce cavitation. Earlier ACIM methods involved two transducers of different frequencies, and they were not able to achieve the desired ACIM zone. It is now possible to generate the ACIM zone using only one transducer with high frequency and low frequency frequencies.

What's the Meaning of SAW (Grade)?

SAW means surface acoustic wave. Surface acoustic wave refers to various model of wave propagation along the surface or interface, different boundary conditions and the conditions of propagation medium can inspire different patterns of surface acoustic wave.

Research Client requested the following quote:

Indeed, we are interested in thin wafers of saphire, alumina (Al2O3), quartz.

Diameter: 4inch

Thickness: anywhere 100-150 microns but reproducible, the best would be 127microns

Doping: undoped, we target the smallest possible tangent loss

Price: the smallest possible

UniversityWafer, Inc. Quoted.

Single Crystal Quartz.
Dia Ori  Thick Pol Primary Flat Brand/Grade SEED TTV Top side Ra Backside Ra
4" Z-CUT 0.20mm DSP One  flat as SEMI standard SAW seedless <10um < 1nm < 1nm
4" Z-CUT 0.20mm DSP One  flat as SEMI standard OPTICAL seedless <10um < 1nm < 1nm

Reference #218230 for pricing

Single Crystal Quartz to Fabricatre Deposited Interdigitated Electrodes

A researcher from a large US university asked for a quote on single crystal quartz wafers for their research:

Interested in ST- cut 4-6'' quartz wafers

What's the difference between the following and I'm still not understanding this clearly- our lab is fairly new to quartz crystal purchases. What is a "mean" and "expressing method"? And, Is the angle related at all to the orientation for deposited interdigitated electrodes?

ST-CUT Angle:42°45' (eqvt ID #: U01-120627-19) Seeded (WITH-SEED) "  and "Seeded Angle42°45'±15', With-Seed. ST cut

And the other options? Specifically, what is special about SAW grade and what does the angle represent?

UniversityWafer, Inc. Replied:

Both of them are the same means with different expressing methods.What's the difference between:

SAW Grade, 42.75° ST-Cut, Seeded

Also this is the same with the above two expressing methods, 42.75°=42°45’.

SAW Grade, 42.75° ST-Cut, Seeded

Explaination: material grade is SAW (surface acoustic wave) grade; 42.75° ST-Cut is one of the quartz cutting method, please refer to the attached file of cutting angle introduction, ST cut wafer is used for SAW devices, and the crystal used is a large-size synthetic quartz crystal with less inhomogeneousness in quality. Seeded means the quartz crystal was growed based on a crystal seed.

Of course not, many cutting orientations with different cutting angles could be used to do deposited interdigitated electrodes, such as 42° ST-Cut, 28° ST-Cut, 32° AT-Cut, and so on.

Gallium Nitride on Sapphire Wafer to Fabricate Acoustic Wave (SAW) Devices

A scientist requested the following:

I want to ask the differentce of the material quality between 2 um GaN wafer and 4 um GaN wafer. I want to use the wafer to fabricate some surface acoustic wave devices. In this way, the material quality such as the uniform is important.

UniversityWafer, Inc. quoted the following:

P-type Gallium Nitride on Sapphire (GaN) with 4~5 um thickness and 10mm diameter. he quality of the wafer is the same. Let us know if you have any questions.

Reference #254146 for pricing

Surface Acoustic Waves for Dual Biosensors for Cancer Cell Detection

A researcher from a a Materials Department at a majore university asked for the following quote:

We are working on dual biosensors for cancer cell detection; surface acoustic waves to detect mass and Graphene field effect transistor to detect electrical charge. For this research project we want to try quartz substrate. Kindly give a quotation for a following order: ST-cut 90˚, Y-axis (Guided Love Wave using Polymer on Quartz) 2 inches diameter and 500µm thick. 50 to 100 samples.

UniversityWafer, Inc. Quoted:

Our ST Cut is 42.75 Degree, are you do need 90 degree? See our quotation below: Crystal Quatz Wafer 2", 500um, ST 90 Degree cut, SSP Quantity: 50 wafers, 100 wafers

Reference #259037 for pricing

Lithium Niobate (LiNbO3) Wafers to Fabricate Surface Acoustic Wave (SAW) Units 

A researcher from a government lab requested a quote for the following:

Dear Chris, LiNbO3 SAW grade wafer, 128° YX I am new to SAW devices and this is my first attempt to fabricate a SAW. Recommendations are welcomed. LiNbO3 SAW grade wafer, 128° YX SAW Wave Propagation is X direction Preferred Dimensions : Diameter or Length - 4 inch diameter or - 4 inch length in X direction (X direction for SAW wave propagation) if shape is rectangular 1 inch in other direction if shape is rectangular Thickness: Prefer 3.0 mm, 2.0 mm is good, 1.0 mm is minimum Surface Condition: SAW grade on one surface (single side polish) Opposite surface (Please make recommendation. A non-polished surface may reduce bulk wave responses in the thickness mode.) Quantity: 2 with options for quantities of 3, 4, and 5 Delivery time is important: What is the shipment or delivery time?

We would like to obtain information of in stock Lithium Niobate wafers, 128 degree Y-Cut, with a diameter 4 inch (100 mm) and a 2.0 mm thickness or greater.

Our objective is to fabricate Surface Acoustic Wave (SAW) units with the wafers we obtain.

We would like to obtain information such in Table form on the availability of

Lithium Niobate wafers, 128 degree Y-Cut, with a diameter 4 inch (100 mm) and a thickness 2.0 mm thickness or greater, single side polished preferred; however both sides polished may be acceptable.
Could you provide a table or items that are currently in stock and could be shipped immediately (overnight) with approximate cost? I believe we would order 4 or more wafers.

I have also heard of Black Lithium Niobate and was told it had the same piezoelectric properties.

Do you have Black Lithium Niobate wafers that would satisfy this request? If so, please list these in Table form as requested above.

UniversityWafer, Inc. Quoted

Diameter Orientation Thickness Pol Material Brand /Grade
100 +/-0.2mm 128° Y-Cut 2.0 +/-0.025mm SSP LiNbO3 SAW
100 +/-0.2mm 128° Y-Cut 2.0 +/-0.025mm SSP Black LiNbO3 SAW

Researcher asked:

Is there a way to quantify or provide more information on the black lithium niobate being less prone to be broken to thermal shock? Maybe there is a coefficient of thermal expansion difference between the two materials; that is, clear versus black. Please provide guidance. Just for confirmation, can you confirm that the clear and black have the same piezoelectric properties? Our application is SAW sensors. We designated Lithium Niobate wafers, 128 degree Y-Cut; should the black Lithium Niobate wafers then be 128 degree Y-Cut? I assume the SAW and other ultrasonic wave modes have the same wave velocity; it that correct?

UniversityWafer, Inc. Replied:

We can provide both White and Black lithium niobate wafers. The black ones are better because it is reduced, meaning it would not likely to be broken with thermal shock. 

However, we do not have LN waers with this thickness in stock. We have 0.35mm~0.5mm thickness 4 inch LN wafers in stock, both white and black ones. Please let me know if you are okay with these thinner wafers. They are of the most standard thicknesses.

Fabrication would take around 3 weeks. The quote for your desired 2mm thickness is as below:


per your cocnerns, please see my answer as follows:
the purpose of blacking process is to overcome the pyroelectriccharges of LN substrates ,
and this technological treatment process that possibly controls the oxygen density of LN wafers
to reduce their bulk resistivity adequately, and make them have the function of neutralizing electrical chartge
so, the black LN wafers are less prone to be broken to thermal shock compare to white ones.
but other physical property are no change including thermal expansion etc.
and of cause black and white LN are with same piezoelectris properties for SAW sensors application.

frankly, the original purpose of designing the blacking process is for thinner wafers like as 0.35mm or thinner
so, as regards your 2mm thickness , white LN wafers are enough.

The HSN code of Lithium Niobate is: 3818.0090.00.

Specification

 Value

Offered Specification

SAW propagation direction

X-axis

± 10 minute

 ok

 

Secondary flat length

 

10 mm ± 3 mm

 ok

Secondary flat Orientation

0 arc

(Parallel to X- axis)

± 5’

 +/-12'

Ra of top polished surface (max)

 

6 A°

 ok

 

Ra of bottom surface

 

250 nm (max)

 ok

 

Scratch length (max)

 

10 µm

 ok

 

Visible Flaws (max)

 

2

 ok

Chips along edge (max)

 

0.5 mm

 ok

Chips along flat (max)

 

0.2 mm

 ok

Reference #255577

What is a SAW Sensor and Applications?

SAW sensors are sensitive to biochemical reactions. They are able to measure the presence of hydrogen gas using an oscillating electrical field. The sensing bilayer interacts with hydrogen gas to produce electro-acoustic effects and mass change. These changes are then converted into an output signal which indicates the presence of hydrogen. The SAW device is excited with an electrical field via a source of excitation. It is also sensitive to salt content.

The first gas-phase sensor was described by King in 1964. King used chromatographic stationary phases to selectively adsorb vapors. Wohltjen and Dessy reported the first analytical application of SAW sensors in 1979. They used the device as a gas-chromatography detector, a thermomechanical polymer analyzer, and as a glass transition temperature sensor. Further, they developed the first high-frequency SAW sensors.

SAW sensors respond to perturbations in wave propagation properties. These perturbations are caused by the interactions between the surface acoustic wave and its surrounding layer. The SAW's surface-normal displacement results from mechanical deformation, electrical potential, and mechanical coupling. In contrast to other types of sensors, SAW devices have limited success in liquid environments. To overcome this problem, a new generation of SAW sensors is aimed at the measurement of chemical reaction processes.

Chemical sensing applications primarily rely on SAW devices, because of their high sensitivity, low cost, and reliability. Most SAW chemical sensors monitor changes in SAW phase velocity and attenuation. The frequency of the signal determines how deep the SAW can penetrate. The deeper the frequency, the lower the penetration depth. Additionally, SAW sensors are sensitive to surface interactions, since most binding events take place at the surface. This makes them a promising candidate for chemical detection.

Video: Surface Acoustic Wave Technologies