LGS Crystals Blanks or Blocks:
|X Direction||5~40mm||Y Direction||5~40mm|
|Z Direction||~80mm||Direction Precision||±20’|
|Direction Precision||±20’||Surface Roughness(Lapped)||Ra=0.3~0.5μm|
Sensor, SAW Wafers:
|Reference Flat||2~15mm||Surface Roughness (CMP single or double sides)||Ra≤1nm|
|Orientation||Following customer specifications|
Langasite crystal possesses some great properties, such as higher electromechanical coupling factor than quartz, no phase transition from room temperature to melt point. Some properties of langasite crystal are shown in Table 1.
Table 1 Dielectric, elastic stiffness constants and their first order temperature coefficients of langasite crystal
|Constant||Relative Dielectric Constant||Piezoelectric Constant (pC/N)||Elastic Stiffness (1011Pa)|
|First Order Temp.Coef. (10-6.K-1)||150||-760||329||-342||-66||204||-75||-335||-94||-63|
Table 2 Comparative properties of piezoelectric crystals
|Properties Crystals||Quartz SiO2||Langasite La3Ga5SiO14||Lithium tetraborate Li2B4O7||Lithium Tantalite LiTa3|
|Electromechanical Coupling Factor K%(BAW)||7.0||15.8||24.0||47.0|
|Frequency Spacing Δf, %||0.25||0.90||4.00||7.00|
|Q-Factor Q, x103||100||50||10||2|
|Temperature Frequency Coefficient TFC, x10-6/°C||0.5||1.6||6.0||4.0|
With the rapid development of the communication technology, the new generation communication system enables people not only to talk, but also to transmit image, data and video. Langasite crystal possesses high SAW properties compared with quartz.which make it to be the most competitive material in this field. SAW properties of langasite and quartz are listed in the Table 3.
Table 3 SAW properties of langasite and Quartz
|SAW Velocity Vef (m/s)||(0º,132.75 º,0 º)3157||(0º,140 º,25 º)2756|
|Second order temp.coef. α2(x10-8/°C2)||-3.2||-6.8|
|Temp. Coef. TTO(°C)||25||23|
|Dielectric Constant (ε)||4.92||27|
|Power flow angle Ф, º||0||0.5|
Lanthanum gallium silicate (referred to as LGS in this article), also known as langasite, has a chemical formula of the form A3BC3D2O14, where A, B, C and D indicate particular cation sites. A is a decahedral (Thomson cube) site coordinated by 8 oxygen atoms. B is octahedral site coordinated by 6 oxygen atoms, and C and D are tetrahedral sites coordinated by 4 oxygen atoms. In this material, lanthanum occupied the A-sites, gallium the B, C and half of D-sites, and, silicon the other half of D-sites.Langasite has its crystal structure belonging to the space group P321, point group 32.
LGS is a piezoelectric material, with no phase transitions up to its melting point of 1470 °C. Single crystal LGS can be grown via the Czochralski method, in which crystallization is initiated on a rotating seed crystal lowered into the melt followed by pulling from the melt. The growth of LGS is primarily along the z direction.The electromechanical coupling coefficient of LGS is higher that of a quartz crystal and lower that of lithium tantalate crystal.
LGS crystals have K^2el.mech. value twice superior to that of a quartz crystal, and their temperature coefficients are equal. This enables the manufacturing of wide band filters with high temperature stability. It is also necessary to note also that the value of propagation velocity of a surface acoustic wave in LGS crystal is considerably lower, this value determines the filter size. When manufacturing quartz-and LGS filters operating at the same centre frequency the geometrical dimensions of LGS filters will be smaller, which meets the requirements of the modern electronics and spares the material.
In terms of piezoelectric applications, although LGS has an electromechanical coupling coefficient three times that of piezoelectric crystals, more than half of the materials are expensive, making it difficult to compete with cheap and large quantities of crystal materials. Its main application is limited to the pursuit of excellence without cost, such as military, aviation, aerospace and other fields.
Langasite crystal (La3Ga5SiO14,LGS), belonging to the space group P321, point group 32, has been reported to be promising new piezoelectric materials for fabrication of surface acoustic wave (SAW) and bulk acoustic wave (BAW) devices. The devices made of langasite crystal could be used at a high temperature up to 900℃ because of its high thermal stability. Hangzhou Shalom EO offers the LGS crystals blanks, polished substrates and wafers upon customer's request.