Advantages of Fine Grain (FG), High Density (HD) Piezoceramics

Background

TRS has developed fine-grained Type II and Type VI piezoceramics (TRS200HD and TRS610HD) which have grain sizes ranging from 1-3 µm and properties equivalent to those of conventional ceramics.

In conventional ceramics, the room temperature dielectric constant, piezoelectric coefficients, and electromechanical coupling all decrease with decreasing grain size due to a reduction in domain orientation variants. This limits the minimum grain size that can be practically achieved. This effect has been compensated in TRS' fine grain ceramics, and a process has been developed at TRS that employs conventional sintering at atmospheric pressure.

Advantages of Fine Grain Piezoceramics

Fine grained piezoceramics offer two main advantages over conventional piezoceramics:

• 30% higher mechanical strength
• improved dielectric strength

These advantages are illustrated in the following applications.

Multilayer Actuators.  

Improved mechanical strength translates to higher manufacturing yields, particularly during the slicing or lapping of thin plates for multilayer actuators. Thinner actuator layers are possible, enabling the use of lower driving voltages. Due to the higher dielectric breakdown strength, fine grain multilayer actuators can be driven at higher electric fields than conventional multilayer actuators; this results in a corresponding 2- to 3-fold increase in strain without sacrificing reliability.

High Frequency Ultrasonic Transducer Arrays.  

The use of piezoceramics with grain sizes of ~ 0.5 µm reduces the ceramic microstructural scale to over an order of magnitude below the current dicing limits (~ 10-15 µm kerfs) for high frequency arrays. Machinability is improved since more grains are present across a given element width. In addition, very high frequency (VHF) arrays are made possible by fine grain ceramics. For example, a 50 MHz linear array requires an element spacing of ~ 15 µm and an element width of ~ 20 µm. This could not be achieved using conventional ceramics.

Multilayer Transducer Elements.  

For single element multilayer transducers having high aspect ratios, low capacitance results in a high electrical impedance that must be matched to the impedance of the transmit/receive circuitry. When fine grain ceramics are used for this application, thinner layers and, therefore, more layers per element height can be realized. This increases the capacitance and lowers the impedance of the array.