Zhang Chenchen, Tadigadapa Srinivas
Materials Research Institute, Department of Electrical Engineering, Penn State University, University Park, PA 16802, USA.
Department of Electrical and Computer Engineering, Northeastern University, Boston, MA 02115, USA.
Micromachines (Basel). 2025 Apr 28;16(5):519. doi: 10.3390/mi16050519.
In this paper, we explore the use of chip-scale blown glass microbubble structures for MEMS packaging applications. Specifically, we demonstrate the efficacy of this method of packaging for the improvement of the lifetime of a ferrofluid-based magnetoviscous magnetometer. We have previously reported on the novel concept of a ferrofluid based magnetometer in which the viscoelastic response of a ferrofluid interfacial layer on a high frequency shear wave quartz resonator is sensitively monitored as a function of applied magnetic field. The quantification of the magnetic field is accomplished by monitoring the at-resonance admittance characteristics of the ferrofluid-loaded resonator. While the proof-of-concept measurements of the device have been successfully made, under open conditions, the evaporation of the carrier fluid of the ferrofluid continuously changes its viscoelastic properties and compromises the longevity of the magnetometer. To prevent the evaporation of the ferrofluid, here, we seal the ferrofluid on top of the micromachined quartz resonator within a blown glass hemispherical microbubble attached to it using epoxy. The magnetometer design used a bowtie-shaped thin film Metglas (FeBSi) magnetic flux concentrator on the resonator chip. A four-times smaller noise equivalent, a magnetic field of 600 nT/√Hz at 0.5 Hz was obtained for the magnetometer using the Metglas flux concentrator. The ferrofluid-based magnetometer is capable of sensing magnetic fields up to a modulation frequency of 40 Hz. Compared with the unsealed ferrofluid device, the lifetime of the glass microbubble integrated chip packaged device improved significantly from only a few hours to over 50 days and continued.
在本文中，我们探索了芯片级吹制玻璃微泡结构在微机电系统（MEMS）封装应用中的使用。具体而言，我们展示了这种封装方法对于提高基于铁磁流体的磁黏滞性磁力计寿命的有效性。我们之前曾报道过基于铁磁流体的磁力计的新颖概念，其中高频剪切波石英谐振器上铁磁流体界面层的黏弹性响应会作为施加磁场的函数被灵敏地监测。磁场的量化是通过监测加载铁磁流体的谐振器的共振导纳特性来完成的。虽然该器件的概念验证测量已成功进行，但在开放条件下，铁磁流体的载液蒸发会不断改变其黏弹性特性，并损害磁力计的寿命。为防止铁磁流体蒸发，在此我们使用环氧树脂将铁磁流体密封在与微加工石英谐振器相连的吹制玻璃半球形微泡内。磁力计设计在谐振器芯片上使用了领结形薄膜美特格拉斯（FeBSi）磁通集中器。使用美特格拉斯磁通集中器的磁力计在0.5 Hz时获得了四倍小的噪声等效值，磁场为600 nT/√Hz。基于铁磁流体的磁力计能够检测高达40 Hz调制频率的磁场。与未密封的铁磁流体器件相比，玻璃微泡集成芯片封装器件的寿命从仅几个小时显著提高到超过50天且仍在持续。
