Abstract
Miniature Microelectromechanical Systems (MEMS) pressure sensors possess various merits, such as low power consumption, being lightweight, having a small volume, accurate measurement in a space-limited region, low cost, little influence on the objects being detected. Accurate blood pressure has been frequently required for medical diagnosis. Miniature pressure sensors could directly measure the blood pressure and fluctuation in blood vessels with an inner diameter from 200 to 1000 μm. Glaucoma is a group of eye diseases usually resulting from abnormal intraocular pressure. The implantable pressure sensor for real-time inspection would keep the disease from worsening; meanwhile, these small devices could alleviate the discomfort of patients. In addition to medical applications, miniature pressure sensors have also been used in the aerospace, industrial, and consumer electronics fields. To clearly illustrate the “miniature size”, this paper focuses on miniature pressure sensors with an overall size of less than 2 mm × 2 mm or a pressure sensitive diaphragm area of less than 1 mm × 1 mm. In this paper, firstly, the working principles of several types of pressure sensors are briefly introduced. Secondly, the miniaturization with the development of the semiconductor processing technology is discussed. Thirdly, the sizes, performances, manufacturing processes, structures, and materials of small pressure sensors used in the different fields are explained in detail, especially in the medical field. Fourthly, problems encountered in the miniaturization of miniature pressure sensors are analyzed and possible solutions proposed. Finally, the probable development directions of miniature pressure sensors in the future are discussed.
Highlights
Pressure is one of the basic physical parameters that is tightly associated with life and production
One electrode of a capacitive pressure sensor on the substrate was formed [60] by selective ion implantation, and silica was deposited as a sacrificial layer
Many eye diseases around the world are related to high intraocular pressure (IOP) [103], which means that the measurement of intraocular pressure is fully essential for the diagnosis and treatment of these diseases
Summary
Pressure is one of the basic physical parameters that is tightly associated with life and production. According to the working principle, pressure sensors can be divided into piezoresistive, capacitive, optical fiber, resonant, and piezoelectric types [4]. The sensitive diaphragms above the cavities are subjected pressure and generated stress. Single crystal silicon (Si), polysilicon (polySi) [7], graphene, and Si3N4 are frequently made into pressure sensitive diaphragms in piezoresistive sensors. An “H”-type resonant beam was suspended on the silicon pressure sensitive diaphragm with four fixing endpoints (Figure 1d). The silicon pressure sensitive diaphragm deformed under the applied pressure, which caused tensile stress and compressive stress to act on the “H”-type resonator. (pera)enTsdsyupPriechaiolntstotornutihccsteuv(rSaoPlltIsaEcg)h.ee(mech)aaTtniycgpdeicitaahlgrrsoaturmugchotuftrhaaepl pisecizehozeeomleealcetticrctircdiciparegeffrsaesmcutr.eo(fsf)eanSpscioaernz.noTeihnleegcAterlilecNcptlrraoeynsesmrurcieocrnsoevsnecsrooteprd.e. The AlN layer converted pressure into the voltage change through the piezoelectric effect. This paper includes a variety of working mechanisms for pressure sensors, including piezoresistive, capacitive, fiber optic, and resonant mechanisms. The development direction of the miniature pressure sensor is given
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