Abstract
We propose a new packaging process for an implantable blood pressure sensor using ultrafast laser micro-welding. The sensor is a membrane type, passive device that uses the change in the capacitance caused by the membrane deformation due to applied pressure. Components of the sensor such as inductors and capacitors were fabricated on two glass (quartz) wafers and the two wafers were bonded into a single package. Conventional bonding methods such as adhesive bonding, thermal bonding, and anodic bonding require considerable effort and cost. Therefore CO2 laser cutting was used due to its fast and easy operation providing melting and bonding of the interface at the same time. However, a severe heat process leading to a large temperature gradient by rapid heating and quenching at the interface causes microcracks in brittle glass and results in low durability and production yield. In this paper, we introduce an ultrafast laser process for glass bonding because it can optimize the heat accumulation inside the glass by a short pulse width within a few picoseconds and a high pulse repetition rate. As a result, the ultrafast laser welding provides microscale bonding for glass pressure sensor packaging. The packaging process was performed with a minimized welding seam width of 100 μm with a minute. The minimized welding seam allows a drastic reduction of the sensor size, which is a significant benefit for implantable sensors. The fabricated pressure sensor was operated with resonance frequencies corresponding to applied pressures and there was no air leakage through the welded interface. In addition, in vitro cytotoxicity tests with the sensor showed that there was no elution of inner components and the ultrafast laser packaged sensor is non-toxic. The ultrafast laser welding provides a fast and robust glass chip packaging, which has advantages in hermeticity, bio-compatibility, and cost-effectiveness in the manufacturing of compact implantable sensors.
Highlights
Hypertension is a major risk factor for cardiovascular disease (CVD) and stroke, causing disability and premature death worldwide
An implantable blood pressure sensor is inserted into blood vessels to directly monitor the blood vessel pressure over a long period of time, and the long-term data can be used for the evaluation of hypertension, heart failure, restenosis, and the efficacy of surgical interventions [4,10]
The local glass melting by the focused ultrafast laser beam associated with volume expansion of the molten pool results in ejection focused ultrafast laser beam associated with volume expansion of the molten pool results in ejection of the molten pool of glass near the subsurface of glass [40]
Summary
Hypertension is a major risk factor for cardiovascular disease (CVD) and stroke, causing disability and premature death worldwide. In order to resolve this issue, it is necessary to reduce the misdiagnosis by removing the erroneous factors providing incorrect measurements such as patient posture, environment, cuff size, and measurement technique and by measuring blood pressure accurately before and after the treatment [2,3]. Sensors 2019, 19, 1801 utilized in favorable conditions, misinterpretation of the blood pressure has occurred due to white coat effects produced by complications such as the patients’ lack of comfort, trauma, and infection [4,5,6]. An implantable blood pressure sensor is inserted into blood vessels to directly monitor the blood vessel pressure over a long period of time, and the long-term data can be used for the evaluation of hypertension, heart failure, restenosis, and the efficacy of surgical interventions [4,10]
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