Study O N Controlled Degradation Encapsulation And Material Degradation Mechanism Of Implantable Devices

Degradable implantable device is an important branch of transient devices.How to achieve long-term stable operation of implantable devices in the human body is the key to future implantable biomedical devices.In this paper,we focus on the related research of encapsulation layers for implantable devices,and the anti-ion penetration characteristics of thermally grown Si O₂,Si₃N₄,and silicon nanomembranes.The silicon nanomembranes were prepared on a glass substrate using a transfer process.In this paper,we explored the degradation characteristics of silicon nanomembranes in PBS solution and HBSS solution.The physical process of material degradation was clarified,and a physical model related to degradation was constructed.For the research of the anti-ion penetration properties of packaging materials,a physical model for the transport of sodium ions in the encapsulation layer was established.The threshold voltage shift of the devices protected by Si O₂,Si₃N₄ and silicon nanomembranes(NM)encapsulation layers was simulated and the results show that the silicon nanomembranes can effectively block the penetration of sodium ions,and the life time of the device protected by the encapsulation layer is determined by the complete degradation of Si NM.Combining the silicon NM with thermal Si O₂ can significantly extend the life time of the protected devices.Therefore,the subsequent package is improved to a full-surface package.Based on the use of a silicon nanomembranes as an anti-ion encapsulation layer,a silicon nanomembranes array with a thickness of 200nm was prepared by transferring the top silicon of the SOI to a glass substrate using a transfer process.Degradation experiments were completed in PBS solution and HBSS solution.The degradation rate in PBS solution at 70?was 91.5nm/day,the degradation rate in PBS solution at 50?was 19.9nm/day,and the activation energy of degradation reaction was 0.73e V.The thickness and degradation time satisfy a linear relationship.Combining the relationship between the degradation rate and the temperature,the degradation rate of the silicon nanomembranes in the 37°C PBS solution is 7.4nm/day.The silicon nanomembranes exhibits the characteristics of non-uniform degradation in HBSS solution at 37?,and the degradation rate is 59.9nm/day.The roughness increases with the degradation time,and the thickness satisfy a linear relationship with degradation time.Based on the controllable degradation rate of silicon nanomembranes,this paper simulates the double-layer encapsulation structure by depositing materials such as Hf O₂ on silicon substrates.The accelerated degradation experiments in 50?and 96?PBS solutions show that the double-layer encapsulation structure can effectively prevent the degradation of the underlying silicon nanomembranes.After a period of degradation,the silicon wafer that is not protected by the top package is significantly degraded.There is still no significant change in the top layer material,and the thickness difference between the top layer packaging material and the silicon wafer continues to increase.The experiment shows that the degradation rate of the silicon wafer at the edge of the top layer is much faster and more difficult to control.Combining the reaction coefficient k and the diffusion coefficient D of the silicon nanomembranes obtained with the experiment of the water molecule and the diffusion coefficient in Hf O₂ in the literature,analyzing the degradation mechanism of the Hf O₂/Si double-layer encapsulation structure,the results show that Hf O₂ can effectively block the penetration of water molecules.The number of water molecules that pass through Hf O₂ per unit time is far less than the consumption of the silicon nanomembranes,therefore,the degradation rate depends on the number of water molecules passing through Hf O₂ per unit time and the mass density of the silicon nanomembranes.When the thickness of Hf O₂and silicon nanomembranes is the same,the lifetime of the double-layer encapsulation structure is the longest.