Temperature Calibration¶
see also IV Curve panel
Overview¶
The NanoFrazor’s cantilever contains integrated microheaters for patterning (“the writer”) and distance sensing (“the reader”). Measurement of the relationship between current and applied voltage for each heater can be used to determine the heater temperature as a function of applied voltage. This relationship is used for optimising the read sensor’s sensitivity and setting the heater temperature during patterning.
Description of the procedure¶
The heat exchange between the cantilever and the surface depends on the distance between the two. Consequently, the relationship between the applied voltage and the heater temperature depends on the cantilever height. Before measuring the current-voltage or “IV” characteristic, the cantilever is positioned at the height which will be used for patterning via the Z piezo. Note that in practice a difference between the patterning height and thermal calibration height of less than 100 nm will not lead to significant errors. Once the cantilever has been placed at the correct height, the NanoFrazor applies a voltage ramp. The heater current at each level of applied voltage is recorded.
Measured Data¶
Results¶
The result of an IV curve on the cantilever’s heaters is shown in figure Figure 9. Initially the current grows linearly with the voltage (ohmic behavior), where the slope is the sum of the resistance of the cantilever and a control resistor in the NanoFrazor electronics. As the temperature of the heater rises, the resistance increases non-linearly because of scattering of the conduction electrons by phonons. At higher temperatures, the silicon forming the heaters enters the intrinsic regime. At high temperatures the intrinsic carriers have enough thermal energy to jump into the conduction band, leading to a reduction in the resistance. These three regimes are visible in the IV curves (purple and blue lines) in Figure 9. At higher voltages, the IV curve is again linear because it is dominated by the resistance of the resistor in series with the cantilever.
Analysis¶
The IV curve data can be used to calculate the heater’s resistance. This resistance has a well defined maximium which depends on the heater’s doping level [Duerig2005]. For the NanoFrazor cantilever, the maximum of the resistance is at 650 °C. The heater temperature for the full range of applied voltages is obtained assuming a linear dependence of the heater temperature on the power dissipated in the heater.