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thermalcond:start [2012/06/25 18:10] – riverthermalcond:start [2020/03/06 09:04] (current) – external edit 127.0.0.1
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 ====== 3-omega Method ====== ====== 3-omega Method ======
  
-Helpful Publications:+==== Heater Deposition ====
  
-  *[[http://rsi.aip.org/rsinak/v61/i2/p802_s1|Thermal conductivity measurement from 30 to 750 K: the 3ω method]] - David G. Cahill; Rev. Sci. Instrum. 61, 802 (1990); doi:10.1063/1.1141498   +Typically, heaters are patterned using the following photolithography procedures: 
-  *Erratum: “Thermal conductivity measurement from 30 to 750 K: The 3ω method” [Rev. Sci. Instrum. 61, 802 (1990)]  Rev. Sci. Instrum. 73, 3701 (2002); doi:10.1063/1.1505652+ 
 +  -  Samples are first cleaned with 18 MΩcm DI water, acetone, methanol, isopropynol, DI water, each in an ultrasonic bath for 15 minutes.  
 +  - Samples are then blown dry with nitrogen and baked at 115 C for two minutes.  
 +  -  PR Primer (S100?) spun onto sample at 3000 rpm for 30 seconds 
 +  -  Soft bake at 85 C for two minutes 
 +  -  S1813 positive photoresist spun on at 3000 rpm for 30 seconds 
 +  -  Soft bake at 85 C for two minutes 
 +  -  The photoresist is exposed through a chrome-quartz mask. This mask should be cleaned to remove dust and other debris prior to putting it in the mask aligner. For Si substrates with thin films, a 6 second exposure at (POWER?) achieves good results.  
 +  -  The PR is developed in (CHEM?) for 15 seconds, followed by an immediate rinse in DI water 
 +  - Hard bake at 115 C for two minutes 
 +  - Samples are sonicated for 15 minutes in 18 MΩcm DI water to remove PR residue 
 +  - Al is deposited by thermal evaporation. Base pressure should be less than 5 uTorr. Substrates are heated to approximately 150 C  during the deposition to assure good adhesion of the Al. If a series of samples is being made, it is advisable to deposit the Al on all heaters simultaneously to achieve consistent TCR and thermal interface results.  
 +  - Samples should be cooled to room temperature before removing from vacuum! Otherwise, the Al will oxidize. 
 +  - Samples are sonicated in acetone to remove the unwanted PR and Al. This lift-off process takes about 5-10 minutes. Acetone residue is removed with IPA and samples are blown dry with nitrogen.  
 + 
 +==== Measurement Software ==== 
 + 
 +Currently, measurements are taken with a LabVIEW VI. The VI communicates with the SR850 lock-in amplifier and an Agilent oscilloscope. The VI cycles the source through a series of applied voltage frequencies and waits for the lock-in measurement of the 3-omega voltage to become stable. It does this by actively measuring (typically with a 100 Hz sample rate) the amplitude of the 3-omega signal and comparing the derivative of this to a user-set threshold. The VI determines the signal is stable when the derivative is below this threshold for a set number of data points (usually around 100). The user can set the derivative threshold and the sample rate from the VI front panel.  
 + 
 +Once the signal is stable, the VI records the in and out of phase 3-omega voltages and the 1-omega rms voltage (channel 1) and current (channel 2) measurements from the oscilloscope. The program auto-scales the oscilloscope window for measurements over the entire frequency range. 
 + 
 +Once the frequency range has been swept, the VI prompts the user for a location to save the data. This data is in a tab separated value format with the following column structure: 1-omega frequency (Hz), in-phase 3-omega voltage (mV), out-of-phase 3-omega voltage (mV), 1-omega voltage (mV), 1-omega current (mA).  
 + 
 +==== Useful Publications ==== 
 + 
 +  *[[http://rsi.aip.org/rsinak/v61/i2/p802_s1|Thermal conductivity measurement from 30 to 750 K: the 3ω method]] - David G. Cahill; Rev. Sci. Instrum. 61, 802 (1990); doi:10.1063/1.1141498; **and** Erratum: “Thermal conductivity measurement from 30 to 750 K: The 3ω method” [Rev. Sci. Instrum. 61, 802 (1990)]  Rev. Sci. Instrum. 73, 3701 (2002); doi:10.1063/1.1505652
   *[[http://avspublications.org/jvsta/resource/1/jvtad6/v7/i3/p1259_s1?isAuthorized=no|Thermal conductivity of thin films: Measurements and understanding]] - David G. Cahill; J. Vac. Sci. Technol. A 7, 1259 (1989); doi:10.1116/1.576265   *[[http://avspublications.org/jvsta/resource/1/jvtad6/v7/i3/p1259_s1?isAuthorized=no|Thermal conductivity of thin films: Measurements and understanding]] - David G. Cahill; J. Vac. Sci. Technol. A 7, 1259 (1989); doi:10.1116/1.576265
   *[[http://www.sciencedirect.com/science/article/pii/S0924424707000441|Extension of the 3ω method to measure the thermal conductivity of thin films without a reference sample]] - J. Alvarez-Quintanaa and J. Rodríguez-Viejo; Sensors and Actuators A: Physical , V. 142-1 (2008); doi:10.1016/j.sna.2007.01.013   *[[http://www.sciencedirect.com/science/article/pii/S0924424707000441|Extension of the 3ω method to measure the thermal conductivity of thin films without a reference sample]] - J. Alvarez-Quintanaa and J. Rodríguez-Viejo; Sensors and Actuators A: Physical , V. 142-1 (2008); doi:10.1016/j.sna.2007.01.013
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 ===== Correspondence ===== ===== Correspondence =====
 +** River's 11/13 email on Al heaters**
 +<code>Aluminum is the way to go for the 3-omega heaters (it is the only material that we've had success with for thin film measurements). 
 +
 +Ram and I tried nickel heaters on tetrahedrite w/ MnS insulating layer; the nickel reacted with the underlying film during dep, resulting in unusable heaters. 
 +In principle, Ni would be better than Al for 3-omega measurements as it has a significantly higher electrical resistivity and temperature coefficient of resistance. 
 +
 +Ram and I made another attempt with Al heaters on tetrahedrite films before I left. The films were extremely rough post-anneal, resulting in broken heaters. </code>
  
 **Email correspondence from Jean-Yves Duquesne of Université Pierre et Marie Curie to River Wiedle (10 May 2011):** **Email correspondence from Jean-Yves Duquesne of Université Pierre et Marie Curie to River Wiedle (10 May 2011):**
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   * Contact pads act as heat sinks! This causes a non-uniform temperature profile across the heater. A few papers have shown that this is not as big of a problem for AC signals above 10 Hz. However, using a heater design that moves the voltage leads away from the contact pads can help to get rid of this problem. Comsol modeling has shown that the voltage leads do not significantly alter the temperature profile of the heater.    * Contact pads act as heat sinks! This causes a non-uniform temperature profile across the heater. A few papers have shown that this is not as big of a problem for AC signals above 10 Hz. However, using a heater design that moves the voltage leads away from the contact pads can help to get rid of this problem. Comsol modeling has shown that the voltage leads do not significantly alter the temperature profile of the heater. 
   * The width of the heater needs to be extremely uniform for accurate measurements. For film measurements, it needs to be measured.   * The width of the heater needs to be extremely uniform for accurate measurements. For film measurements, it needs to be measured.
 +  * FIXME Information about making masks for heater KAI please add
  
 ==== Automation ==== ==== Automation ====
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 ====== People ====== ====== People ======
 The system was set up in 2011 by River Wiedle in collaboration with Mark Warner. The system was set up in 2011 by River Wiedle in collaboration with Mark Warner.
-Matt Oostman worked on the project Fall 2011->  Nico Schmidt Spring 2012 ->+Matt Oostman worked on the project Fall 2011->2012  Nico Schmidt Spring 2012 -> Fall 2012

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