This paper reviews the research and development of micromachined accelerometers with a noise floor lower than 1 µg/√Hz. Firstly, the basic working principle of micromachined accelerometers is introduced. Then, different methods of reducing the noise floor of micromachined accelerometers are analyzed. Different types of micromachined accelerometers with a noise floor below 1 µg/√Hz are discussed. Such sensors can mainly be categorized into: (i) micromachined accelerometers with a low spring constant; (ii) with a large proof mass; (iii) with a high quality factor; (iv) with a low noise interface circuit; (v) with sensing schemes leading to a high scale factor. Finally, the characteristics of various micromachined accelerometers and their trends are discussed and investigated.

This paper presents an optimized way of lead zirconate titanate (PZT) deposition in orderto selectively grow three different (100/001), (110), and (111) crystal orientation in two differentthickness ranges, thinner and thicker than 400 nm. The thickness of the PZT layer is also optimizedto not diminish the generated bending moment more than 10%. A 1μm PZT layer with (100/001)dominant crystal orientation and highly columnar crystal structure is deposited and used in thefabrication of a circular PMUT. The PMUT has a 410 μm diameter and resonates at 462 kHz withthe displacement of 1200 nm/V.

This paper presents the design and fabrication strategy of a lead zirconate titanate (PZT)based piezoelectric micromachined ultrasound transducers (pMUT) with the objective of maximizing its performance. Choosing the most suitable thickness of the PZT layer, the radius of the top electrode, and the effect of the residual stress on the resonance frequency of a pMUT are investigated by finite element method (FEM) simulation and analytical equations. Three different architectures of pMUTs are presented: (i) a pMUT with a top center electrode, (ii) a pMUT with a top center and ring electrode, (iii) a pMUT with a patterned PZT layer. All three pMUT architectures were fabricated and their displacement response, resonance frequency, and Q-factor are compared. The fabricated pMUT in all three architectures has a radius of 205 µm, a Si membrane thickness of 6 µm, and a PZT thickness of 1 µm. The experimental results were compared to FEM simulation. The proposed architectures have a displacement response of 6.6 µm V −1 , 7.5 µm V −1 , and 8.6 µm V −1 , respectively, for their optimum design parameters.

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