Design and fabrication strategy for an efficient lead zirconate titanate based piezoelectric micromachined ultrasound transducer

Abstract

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.

Mixed Nonlinear Response and Transition of Nonlinearity in a Piezoelectric Membrane

“…A similar tuning in resonant frequency due to change in strain has been reported in doubly clamped membranes, 44 beams, and PMUTs. 45,46 The resonant mode at 169.1 kHz is confirmed to be fundamental mode by mapping the mode shape (Figure S3). The dynamic response of D3 before (b 2 = 0.1006 and b 3 = 0.0180) and after annealing is shown in Figure 5b,c, respectively.…”

Novel Phased Array Piezoelectric Micromachined Ultrasound Transducers (pMUTs) for Medical Imaging

“…Transmission sensitivity is related to the output acoustic power per unit of input electrical power. It has been previously demonstrated that in order to have sufficient output acoustic power, the lateral dimension of the pMUT membrane should be equal to or bigger than half of the transmitted wavelength [16]. Therefore, based on the desired working frequency, lateral dimensions and the thickness of the membrane are optimized.…”

“…The capacitance of an element together with the parasitic resistors form a low pass filter with a bandwidth of 1/2RC. If the resonance frequency of the transducer is higher than this value, most of the input electrical power is consumed to charge and discharge the capacitor [16]. Hence, for the high frequency pMUTs an additional polyimide dielectric layer is introduced on top of the PZT layer, which works as an insulating layer, to reduce the parasitic capacitance.…”

“…The pMUT arrays were fabricated based on the bulk micromachining process, as shown in Fig. 2 [16]. In the first step, (a) about 250 nm Ti/Pt was deposited on an SOI wafer as the bottom electrode.…”

“…Moreover, the membrane thickness in cMUTs is limited to a thickness of maximum of about 2 µm, first because they have relied on surface micromachining fabrication techniques, and second because the weak electrostatic 2 should be able to bend the membrane. As a result, the lateral dimension of a cMUT is often very small to achieve a certain resonance frequency, which results in a low output acoustic pressure and sensitivity [16]. Consequently, cMUTs suffer from low image quality, especially in applications that require a high depth of penetration.…”