NEWS REVIEW We bring quality to light.
Doped tungsten doubles lifetime in sapphire growth
PLANSEE USES the creep-resistant tungsten material ‘WVM’ to manufacture heaters for sapphire growth. These have more than twice the service life of conventional tungsten heaters.
LED test & measurement
Solutions from the world leader
Instrument Systems continues to set the benchmark in LED metrology. Whether testing individual LEDs (standard or high-power), LED modules, or OLEDs – the global LED industry relies on us to engineer superior measurement equipment for high-speed production testing and high-performance R&D and QC applications.
Sapphire growth takes place at high temperatures of approximately 2100 °C. In the Kyropoulos process, rod heaters made from pure tungsten are generally used. These often have to be replaced after just a few cycles. This is due to the high level of embrittlement and deformation. It can sometimes be so extreme that the heater rods touch the shielding and cause short-circuits. To meet the needs of single crystal growth applications, Plansee has further developed a material that has already earned the plaudits of the lighting industry for its behaviour at high temperatures.
The material consists of pure tungsten with very low quantities (30-70 ppm) of potassium. The creep resistance of this material is several times better than that of pure tungsten. This capability was recently confirmed by a sag test performed by Plansee’s materials engineers.
The scientists at Plansee simulated the use of its novel material at high temperatures and under various mechanical loads. The sag test proved that WVM sags four times less than pure
tungsten. This is because potassium leads to a more stable and coarser crystalline structure than pure tungsten. This property also has a positive influence on the material’s creep resistance. The graph below compares the sag for pure tungsten and WVM.
Samples used in the analysis obtained from the graph above were tested at 2100 °C, for 6 hours with a bending stress of 22 MPa.
Plansee says rod heaters,
mesh heaters, and sheet heaters made from WVM provide excellent dimensional stability, especially when it comes to high-temperature processes such as sapphire growth.
While conventional tungsten heaters have to be replaced after just a few cycles, WVM heaters are claimed to easily last for 2 to 3 times as long.
Rod type heater used in sapphire growth At 99.97 percent, the purity of WVM is the same as that of pure Plansee tungsten. The potassium content in WVM is firmly bound in the material. As a result, it will not contaminate the furnace atmosphere. The material is suitable for use in extremely sensitive high-vacuum processes in the same way as pure tungsten.
But when it comes to sapphire growth, Plansee believes it is able to offer more than hot zones with particularly durable heaters. The company also produces the corresponding pressed-sintered tungsten crucibles. These high purity crucibles have an ultra-smooth surface.
light measurement
www.instrumentsystems.com
The sapphire can be extracted without difficulty from the crucible without any damage to the crucible surface. And the smooth surface is less susceptible to corrosion in contact with the sapphire melt. With their high and homogenous density of over 93 % the crucibles are non-deformable even at high and rapidly changing temperatures.
IS_Ad_Image
blau_58x247.indd 1
8
www.compoundsemiconductor.net August / September 2013 07.02.13 13:10
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104 |
Page 105 |
Page 106 |
Page 107 |
Page 108 |
Page 109 |
Page 110 |
Page 111 |
Page 112 |
Page 113 |
Page 114 |
Page 115 |
Page 116 |
Page 117 |
Page 118 |
Page 119 |
Page 120 |
Page 121 |
Page 122 |
Page 123 |
Page 124 |
Page 125 |
Page 126 |
Page 127 |
Page 128 |
Page 129 |
Page 130 |
Page 131 |
Page 132 |
Page 133 |
Page 134 |
Page 135 |
Page 136 |
Page 137 |
Page 138 |
Page 139 |
Page 140 |
Page 141 |
Page 142 |
Page 143 |
Page 144 |
Page 145 |
Page 146 |
Page 147 |
Page 148 |
Page 149 |
Page 150 |
Page 151 |
Page 152 |
Page 153 |
Page 154 |
Page 155 |
Page 156 |
Page 157 |
Page 158 |
Page 159 |
Page 160 |
Page 161 |
Page 162 |
Page 163 |
Page 164 |
Page 165 |
Page 166 |
Page 167 |
Page 168 |
Page 169 |
Page 170 |
Page 171 |
Page 172 |
Page 173 |
Page 174 |
Page 175 |
Page 176 |
Page 177 |
Page 178