Development of Temperature Sensor Based on AlN/ScAlN SAW Resonators

Round 1

Reviewer 1 Report

Thank you for the submission. I am trying to understand the novelty of this paper. Temperature sensors based on SAW resonators have been known for decades (https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=1454474). My perception is that the authors want to compare traditional SAW temperature sensors based on LiNO3 or Quartz with a new SAW temperature sensor based on AlScN. If this is the case, they should provide a table that compares these two technologies in terms of temperature coefficient of frequency (TCF), size, number of fabrication masks, etc. Perhaps, they may want to include other types of piezoelectric resonators as well, such as FBAR or SMR.

Comment 1: Authors report the measured TCF in units of kHz/C in the Abstract. However, most MEMS engineers report this value in terms of ppm/K (parts-per-million per Kelvin), which is independent of resonance frequency. Can the authors replace the units?

Comment 2: Applying three different methods to measure the same magnitude (TCF) is redundant. Instead, it is critical to ensure that the selected method has enough resolution and accuracy. In my opinion, the most adequate technique to determine TCF is the direct method using a network analyzer. For that reason, I would just report the TCF extracted with this method, and modify the paper to state that this value was used to validate the implementation of the SAW resonator in an oscillator and a wireless system to detect temperature.

 

Comment 3: To figure out the specific mode of vibration exhibited by the SAW resonator of study (e.g., Rayleigh), Figure 2 should include the COMSOL simulation of displacement.

Comment 4: The Device and fabrication of SAW resonator section is poorly written and should provide more details. In terms of design, the authors should provide the IDT pitch, the number of reflectors, the measured Q and kt2 values, and explain why they target 446MHz instead of other resonance frequency. In terms of fabrication, they should explain why they select specific material thicknesses, combine AlN and AlScN instead of using only AlScN, etc.

Comment 5: The Device and fabrication of SAW resonator section should also include simulations of frequency vs. temperature for different SAW resonator frequencies and material compositions. The authors are trying to “outsell” the advantages of using AlScN/AlN over other piezoelectric materials to build SAW temperature sensors. Therefore, they need to demonstrate that they have methodically selected the best design.

Comment 6: There is no scientific interest in building an oscillator and a wireless sensor with a SAW resonator. Again, TCF should be measured with a network analyzer and used to validate that the oscillator and wireless sensor work properly. However, the relevant information that these experiments can provide are: 1) the minimum detectable signal (MDS) in degrees that the SAW resonator can detect, and 2) the maximum distance at which the sensor can be interrogated with the wireless transponder. Other important pieces of information are linearity, accuracy, dynamic range, etc.

Comment 7: Figure 6 should provide measurement error in %.

N/A

Author Response

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Reviewer 2 Report

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Reviewer 3 Report

The manuscript proposes a temperature sensor based on SAW resonator. The manuscript comprises  analytical model and experimental measurement. The following points have to be addressed:

1. The authors have to mention why in GSG port two ground are shorted and system has no a common ground?

 2. Fig 2 shows a very strang shape of SAW resposne? The system has a quality factor and works as a resonator? please clarify it.

3. The authors have nor report any info about S parameters. So, S11 and S12 are required beside of impedance. 

4. Further information about size of reflectors have to be provided. Why the reflectors are larger than the SAW it self. 

5. Line 76, it is mentioned that 100um thick aluminium is deposited. How possible to deposit such a thick Al? 

6. Fig3 (d) indicates that the curve fitting is done based on BVD model with a quality factor of 2029. This is a high Q for SAW system.

proof reading is needed 

Author Response

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Round 2

Reviewer 1 Report

Thank you for addressing my previous comments. I believe the manuscript has greatly improved after the added modifications. However, I still a couple of extra comments:

Comment 1: The authors report COMSOL simulations of AlN, AlN/ScAlN and ScAlN -based SAW resonators and claim that the best Q is obtained for AlN/ScAlN. However, as you know, Q can be due to different loss mechanisms: acoustic losses, electrical losses, material losses, surface losses, etc. What type of losses and how are they simulated? You will need to provide full detail. 

Comment 2: The authors report a wireless interrogation method to compute TCF. However, with this method, they are not directly measuring resonance frequency, but rather ring-down time response. Please, provide the equation used to calculate frequency from time response. How long do you need to wait to accurately measure ring down? Is 5us enough and why?

 

Author Response

Every comment you give is very helpful, thanks for the suggestions. Please see the attachment for the latest reply.

Author Response File: Author Response.pdf

Reviewer 3 Report

The authors have addressed my comments.

Good

Author Response

Thanks for your helpful comments.