Across countries, cultures, and societies, healthcare is a driving force of prosperity and life. Healthcare funding, advancements, and efficacy have a direct link to the quality of life in modern society. As healthcare advances, lives are saved.
As a result, healthcare alone constitutes over 21% of global R&D spending. New technologies, procedures, and pharmaceuticals are always on the verge of completion, and the healthcare industry is on the cusp of a major breakthrough every day. Plasma processing technology (i.e., dry etching and deposition tools) has enabled many of those advances in healthcare — specifically in bioMEMS.
MEMS, Healthcare, and Plasma Processing
Micro Electro Mechanical Systems (MEMS) are micro-scale, electrical or mechanical systems that are made with microfabrication technology. MEMS encompasses a large field of devices, and they can range from simple to highly complex at the micro-scale. MEMS can have microsensors and microactuators, both of which allow them to process information and understand their environment. BioMEMS are MEMS used in the medical/pharmaceutical industry (primarily for biomedical research and medical microdevices), which are expected to reach $6.9B in industry value by 2023 (CAGR 14.9% from 2017 - 2023).
The fabrication of bioMEMS relies on dry etching and deposition tools that can etch microscopic structures. Deep Reactive Ion Etching (DRIE) is capable of etching vertical holes and trenches in silicone films and microstructures. Plasma Enhanced Chemical Vapor Deposition (PECVD) tools are used during the deposition process of films. Often deep RIE and PEVCD are used in combination during the fabrication process. PEVCD oxide coating can help prevent the notching effect of DRIE. The exact dry etching and deposition tools used to fabricate bioMEMS differ depending on the needs, structure, and materials of the product.
Among the many applications of bioMEMS, five stand out as revolutionary:
Unlike conventional hypodermic needles, microneedles are small enough to only penetrate the epidermis — avoiding patient pain associated with penetration into the dermis layer. Microneedles are formed in an array, allowing them to distribute medicine painlessly and rapidly without the need for significant physician attention and training. In other words, microneedles are bloodless, painless, and efficient. The Bill and Melinda Gates Foundation, Koch Institute, and MIT have all donated, studied, and collaborated on microneedles.
In fact, microneedle vaccines (which are a subject of heavy research) have recently been studied to fight COVID-19. The National Institutes of Health (NIH) recently released findings regarding the microneedle COVID-19 vaccine they funded. So far, the results look promising.
In addition to lithography, microneedles are traditionally fabricated using RIE. Inductively coupled plasma reactive ion etching (ICP-RIE) is commonly used to yield straight-walled holes through silicon wafers during the fabrication process. This is detailed in a PNAS study.
In addition to microneedles, other bioMEMS promise to change the landscape of drug delivery. Microreservoirs — which are microstructures with a reservoir that release a specific amount of drug into the patient's system — can be implanted into patients to administer the appropriate amount of drug. More importantly, both microneedles and microreservoirs can be connected to smart systems to improve efficacy and accuracy.
In one recent study, researchers used both microneedles and microreservoirs to administer drugs behind an eye patch to treat corneal neovascularization. Like microneedles, microreservoirs rely on RIE etching during their fabrication process.
Micropumps are MEMS used across the bioMEMS field for a variety of applications. As the name suggests, micropumps are microscopic pumps used to move microfluids. Some common uses of micropumps include:
- Glucometers: Many companies use micropumps to subcutaneously deliver insulin through glucometers. These pumps are connected to sensors in the device, and those sensors regulate the micropump activity — resulting in a consistent dosage.
- Insulin pumps: Like glucometers, insulin pumps are used to combat diabetes. With insulin pumps, insulin is fed regularly into the body, mimicking the human pancreas. Typically, insulin is provided at regular intervals during the day at a basal rate as well as after meals.
Deep RIE is also used to fabricate micropumps, especially in silicone applications.
Lab-on-a-chip is another MEMS technology that has disrupted the bio space. These small, microscopic chips can integrate multiple laboratory functions at microscale. Microfluid chambers in these chips can be connected with sensors to create smart and efficient lab processes that are cheap, effective, and hyper-scalable.
DRIE is a critical component of the lab-on-a-chip manufacturing process. DRIE can fabricate multilevel microstructures at full-wafer scale. Depending on the application, many microfluidic chips rely on DRIE to etch wafers.
Perhaps the most interesting, groundbreaking, and novel bioMEMS application is organ-on-a-chip technology. These contain hollow microfluidic channels with living human organ cells. The mechanical properties of the MEMS can be adjusted to simulate the living environment of organs.
Currently used in research applications, organ-on-a-chip technology promises to disrupt in vitro care, biomedical research, and cellular cultures. For example, researchers are using organ-on-a-chip MEMS to study the impact of smoking on organ biology. Other researchers are investigating personalized medicines using these chips as stand-ins for organs.
To construct organ-on-a-chip MEMS, photolithography is used to produce silicone wafer structures. RIE is then used to etch away any excess materials for accuracy.
These five applications of plasma processing technology are only the cusp of what is possible with dry etching and deposition tools. For example, while PECVD and low pressure CVD (LPCVD) have been extensively used in medicine, more advanced technology such as High Density Plasma - Chemical Vapor Deposition (HDPCVD) remains available.
Learn more about the differences between HDPCVD, PECVD, and LPCVD by downloading our whitepaper “Comparing Chemical Vapor Deposition Systems.”