Doping-Induced Temperature Compensation of Thermally Actuated High-Frequency Silicon Micromechanical Resonators

Hajjam, Arash; Logan, Andrew S.; Pourkamali, Siavash

doi:10.1109/jmems.2012.2185217

Cited by 38 publications

(17 citation statements)

References 18 publications

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“…Figure 5 shows the temperature drift characteristics of the same resonator measured before and after each of the oxidation steps. Silicon resonators typically exhibit temperature coefficient of frequency (TCF) in the -20 to -40 ppm/°C range [10], [11]. Figure 5 shows that while the initial TCF for this resonator was measured to be -37 ppm/°C, its value has gradually increased (become less negative) after each oxidation step.…”

Section: Measurement Resultsmentioning

confidence: 98%

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Self-Contained Frequency Trimming of Micromachined Silicon Resonators via Localized Thermal Oxidation

Hajjam

Pourkamali

2013

J. Microelectromech. Syst.

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An electronically controllable frequency trimming technique based on localized thermal oxidation of single crystalline silicon resonators is demonstrated. Thin layers of silicon dioxide can be thermally grown on silicon surfaces of resonant structures via extreme joule heating of such when biased with relatively large bias currents in an oxygen-rich environment. Changes in structural stiffness or oxidation induced internal stress causes a shift in the resonant frequency of the structures that can be used for post-fabrication frequency trimming of silicon resonators. As an added advantage, the positive temperature coefficient of Young's modulus for the added silicon dioxide layer can partially compensate the large negative temperature coefficient of frequency (TCF) for the silicon resonators. Frequency trimming as high as ∼3.7% and TCF as low as 0.2 ppm/°C has been demonstrated for a 54 MHz I-shaped resonator using this technique. Furthermore, it has been demonstrated that coupling of mechanical resonance to electrical resistance and consequently joule heating of the structure can lead to a cooling effect at mechanical resonant frequency of the structure that allows the localized oxidation to stop automatically as soon as the resonator frequency reaches a targeted actuation frequency applied to the structure. The viability of this concept is demonstrated by application of both off-resonance and at-resonance actuation signals to fabricated resonators showing that as opposed to the off-resonance signals, the at-resonance signals with the same intensity do not lead to further frequency shift.[2012-0337]

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Section: Measurement Resultsmentioning

confidence: 98%

“…The resonators utilized in this work are referred to as I-shaped Bulk Acoustic Resonators (also known as dog-bone resonators) [9,10]. The schematic view of an I-shaped resonator is shown in Figure 1a.…”

Section: Resonator Description and Fabricationmentioning

confidence: 99%

Self-Contained Frequency Trimming of Micromachined Silicon Resonators via Localized Thermal Oxidation

Hajjam

Pourkamali

2013

J. Microelectromech. Syst.

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“…The single mask fabrication process for thermally actuated MEMS resonators has previously been extensively explained [15]. This process was used to batch fabricate the resonators This work was supported by National Science Foundation (NSF) under grants #0923518 and #1056068. on a low resistivity SOI substrate with both device layer and BOX thickness of 5µm.…”

Section: Fabrication Processmentioning

confidence: 99%

“…The thin actuator beams of the structures simultaneously act as both thermal actuators and piezoresistive sensors. The operating principle for the resonators has been thoroughly explained in [15]. Figure 2 shows the schematic diagram of the test setup used for characterization of the sensory behavior of the resonators towards changes in relative humidity.…”

Section: Fabrication Processmentioning

confidence: 99%

MEMS resonant human breath sensors for survivor detection in disaster areas

et al. 2012

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This work demonstrates the potential of micromechanical resonators as compact human breath detectors. Such sensors can be mounted on robotic platforms used in search and rescue missions for detection of survivors in disaster areas. Human breath carries higher concentrations of both moisture and carbon dioxide (CO 2 ) compared to surrounding air. To implement the sensors, single crystalline silicon resonators with frequencies in the MHz range were coated by thin films of polyethyleneimine (PEI), which is a strong absorbent of both moisture and CO 2 . The detection mechanism is based on the frequency shift caused by the added mass from the absorbed molecules. The resonators were tested in a humidity controlled chamber showing sensitivity towards humidity as high as 79 ppm/%RH from 30 to 58 %RH and 1.2 286 ppm/%RH from 58 to 85 %RH at room temperature. The response of the same coated resonators to CO 2 was also characterized showing an overall frequency shift of 3010 ppm. Finally, the resonators were exposed to human breath samples and showed frequency shifts as high as 1020ppm with response time constants around 10 seconds.

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“…Tuning via an electrostatic stiffness change, where the stiffness can be adjusted electrostatically with nonlinear capacitive transducers has also been used as a common frequency tuning method [11]. It has also been shown that the resonant frequency of thermally actuated resonators can be finely tuned by changing the actuation DC bias current [12]. MEMS resonators mostly make use of electrostatic (capacitive) [13] or piezoelectric [14] electromechanical transduction.…”

Section: Introductionmentioning

confidence: 99%

Electrostatic frequency tuning of thermal piezoresistive MEMS resonators

Hajjam

Rahafrooz

Pourkamali

2012

2012 IEEE International Frequency Control Symposium Proceedings

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This paper presents a new technique for electrostatic tuning of the resonant frequency of in-plane thermal piezo-resistive micro-electromechanical resonators. The tuning method is based on applying a DC bias voltage between the underlying SOI handle layer and the suspended resonant structure. The DC bias voltage produces an electrostatic force which causes the bending of the resonant structure in the out of plane direction. The resulting stress in the structure causes a shift in its resonant frequency. The experiments were taken place under both atmospheric pressure and partial vacuum. Maximum upward and downward frequency shifts of +580ppm and -430ppm have been demonstrated. As a side product, due to minimized air damping, more than 2X resonator Q improvement was observed while tuning the resonator frequency. I. INTRODUCTIONWith the advances in micromachining technologies, various types of MEMS resonators with a wide range of frequencies from tens of kHz to a few GHz with high quality factors have been demonstrated [1,2]. A variety of microscale electromechanical resonators have been considered/used in various applications such as sensitive and highly integrated chemical [3] and environmental sensors [4], filters [5] and gyroscopes [6]. Arrays of such resonators can be batch fabricated at high quantities at a very low cost. The resonance frequency of silicon micromechanical resonators is dependent on the physical dimensions of the resonating structure. Process variations across the substrate (e.g. non-uniformities in photolithography, etching and film thickness) leading to variations and mismatch in the mechanical resonant frequencies are a major challenge for batch fabrication of micromechanical resonators. Postfabrication trimming is one of the ways to solve this issue. The post-fabrication frequency trimming methods make irreversible permanent changes to the frequency of the devices. Different frequency trimming techniques for MEMS silicon based micromechanical resonators have been presented. The techniques range from pulsed-laserdeposition/trimming [7], gold diffusion into the bulk of the resonator [8] and localized thermal oxidation [9].

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Doping-Induced Temperature Compensation of Thermally Actuated High-Frequency Silicon Micromechanical Resonators

Cited by 38 publications

References 18 publications

Self-Contained Frequency Trimming of Micromachined Silicon Resonators via Localized Thermal Oxidation

Self-Contained Frequency Trimming of Micromachined Silicon Resonators via Localized Thermal Oxidation

MEMS resonant human breath sensors for survivor detection in disaster areas

Electrostatic frequency tuning of thermal piezoresistive MEMS resonators

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