MEMS ile entegre mikro ısıtıcı ve IDE mikro sistemlerin fabrikasyonu ve nano kompozit yarı iletken gaz sensör uygulaması
Fabrication of integrated micro heater and ide micro systems with MEMS and application of nano composite semiconductor GAS sensor
Yazar: HALİME İLBEYİİLİNGİ
Danışman: DR. ÖĞR. ÜYESİ BERNA MOROVA ; DOÇ. DR. CİHAT TAŞALTIN
İstanbul Teknik Üniversitesi / Lisansüstü Eğitim Enstitüsü / Fizik Mühendisliği Ana Bilim Dalı / Fizik Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2024
Konu: Fizik ve Fizik Mühendisliği = Physics and Physics Engineering

Özet:
Günümüzde Mikro Elektro Mekanik Sistemler (MEMS) teknolojisi ile mikro ısıtıcı
sistemlerin inter dijital elektrotlar (IDE) ile entegrasyonunun geliştirilmesine yönelik
ihtiyaç gün be gün artmaktadır. MEMS teknolojisi, mikroskopik ölçekte mekanik ve
elektronik bileşenlerin entegrasyonunu içerir. Mikrosistem mühendisliği, elektronik,
kimya, biyoloji ve fizik gibi birçok farklı disiplini birleştirir. Bu entegrasyon, daha
karmaşık sistemlerin ve uygulamaların geliştirilmesini mümkün kılar. Örneğin,
kimyasal algılama için kullanılan sensörler, biyolojik materyallerle birleştirilerek
hastalık tespitinde kullanılabilir. Bu tür çok disiplinli çalışmalar, araştırma ve
geliştirme süreçlerini zenginleştirir ve bilim ile mühendislik arasındaki sınırları aşarak
yenilikçi çözümler üretir. Bu teknoloji, yüksek hassasiyet ve düşük maliyet avantajları
ile öne çıkarak, biyomedikal uygulamalar, tüketici elektroniği gibi bir çok alanda
kullanılmaktadır. MEMS teknolojisinde kullanılan gaz sensörleri, endüstriyel
süreçlerin kontrolü, hava kalitesinin izlenmesi, çevresel güvenlik ve tıbbi teshişler için
hayati öneme sahip alanlarda kritik rolller üstlenmektedir. Özellikle, endüstriyel ve
çevresel uygulamalarda zararlı gazların tespit edilmesi, halk sağlığı ve güvenliği
açısından büyük öneme sahiptir. Bu nedenle, düşük maliyetli, yüksek duyarlılık ve
hızlı yanıt süresine sahip gaz sensörlerine duyulan ihtiyaç büyüktür. Bu sensörler
biyomedikal uygulamalarda, solunum yolu hastalılarının teşhisinde öneme sahip
uçucu organik biyo belirteçlerin (VOC) tespitiden kanser tipine kadar geniş bir
kullanım alanına sahiptir.
Bu çalışmada tek bir silikon yonganın üzerine ince film biriktirme yöntemlerinde
kullanılan; çok katlı foto-litografi, PVD (e-beam), PECVD, elektrokimyasal
yöntemler, üst üste entegrasyon, ICP-RIE kuru aşındırma, metalizasyon gibi
yöntemler kullanılarak bir çok uygulama alanında kullanılabilir platformlar
üretilmiştir. Üretilen platformun çalışıp çalışmadığının kontrolü için gaz sensör
uygulaması seçilmiştir. İlgili malzemelerin sentez, katkılama ve platform üzerine
kaplanması için hidro termal ve damlatma metodları ile gaz sensörleri üretimi başarılı
bir şekilde gerçekleştirilmiştir.
Çalışma sonucunda 2.2 mm en ve 4.8 mm boy oranlarına sahip, 300 µm Si-yonga
üzerine çok katlı (2 µm SiO2 / 30 nm Ti / 30 nm Au / 600 nm Pt ) mikro ısıtıcı
sistemleler üretilerek, 1 dakikada max 417℃ sıcaklığa yükselen platin mikro ısıtıcılar
üretilmiştir. Platin mikro ısıtıcıların sıcaklık karakterizasyonları için hem kendi
oluşturduğumuz devre hem de termal kamera ile ölçümler yapılmıştır. Ölçüm
sonuçlarından, sıcaklık değişimine karşı direnç değişim grafiğinden platin metali için
α sabiti 0.00345 ℃-1 olarak hesaplanmıştır. Üst üste biriktirme teknolojisi sayesinde
250 nm kalınlığında Si3N4 pasivasyon malzemesi kullanılarak ve üretilen mikro
ısıtıcıların 200℃ ve 400℃ de 2 saat tavlama işlemi gerçekleştirilmiştir. Çok katmanlı
xxvi
(100 nm Ti / 100 nm Au) IDE'lerin üretimi ve Si3N4 ara katman üzerine entegrasyonu
gerçekleştirilmiştir. Bu platform için 4 çıkışlı 2 si mikro ısıtıcı, 2 si IDE sistem çıkışlı
bakır PCB'ler üzerine ilk olarak mikro ısıtıcı sistemlerin ısı kaybını önlemek için 2
mm en ve 2 mm boya sahip 300 µm kalınlığında Si-yonga (wafer) takoz kesimi
gerçekleştirilip üst üste yapıştırılmıştır, ardından tel bağlama (wire bonder) tekniği ile
25 µm Au teller ile bond işlemleri gerçekleştirilmişitir. Gaz sensör uygulaması için
elektro aktif polimer ve metal oksitler kullanılmıştır. PANI, SnO2 malzelemelerin
sentez kısımları gerçekleştirilmiş (PANI için emeraldin baz yalıtkan formu HCl ile
muamele edilerek iletken hale getirilmiştir) ve ticari olarak satılan ZnO malzemesi ile
1:1 mg ve 1:5 mg gibi farklı oranlarında PANI, PANI / SnO2, PANI / ZnO nano
kompozit metal oksit 3 tip gaz sensörleri üretilmiştir. Bu gaz sensörleri ile gaz sensör
uygulamasının; endüstriyel süreçlerin kontrolü, hava kalitesinin izlenmesi, çevresel
güvenlik için öneme sahip NO2 gazı ve solunum yolu hastalıkları için öneme sahip
olan aseton, etanol, nem ve kloroform gazlarının akım-zaman yanıt grafikleri
MATLAB kodu geliştirilerek analiz edilmiştir. Tüm sensörlerin saf gazlara karşı ve
bu saf gazların %30, %50, %70 neme maruz bırakılmış konsantrasyonları için, oda
sıcaklığında ve 55℃ sıcaklıkta ölçümler alınarak bar grafikleri elde edilmiştir.
Platin metali için α sabiti 0.00345 ℃-1 olarak hesaplanması çok katmanlı mikro ısıtıcı
sistemlerin doğru bir biçimde geliştirildiği, 2 mm – 2 mm (en-boy) oranlarındaki
takozların sisteme yapıştırılması ısı kaybını önlemiştir ve max 417℃ sıcaklık elde
edilmiştir. Üretilen 3 sensör tipinin çalışır durumda olduğu ölçüm sisteminden alınan
verilerin MATLAB analizi ile çalışır durumda olduğu tespit edilmiştir.

Abstract:
In recent years, the need for the development of micro heater systems integrated with
interdigital electrodes (IDE) using Micro Electro Mechanical Systems (MEMS)
technology has been increasingly recognized. MEMS technology involves the
integration of mechanical and electronic components at a microscopic scale.
Microsystem engineering encompasses a wide range of disciplines including
electronics, chemistry, biology, and physics. This integration enables the development
of more complex systems and applications. For instance, sensors used for chemical
detection can be combined with biological materials for disease detection. Such
multidisciplinary efforts enrich research and development processes, producing
innovative solutions that transcend the boundaries between science and engineering.
This technology stands out for its high precision and low-cost advantages and is used
in various fields including biomedical applications and consumer electronics. Gas
sensors utilized in MEMS technology play critical roles in areas such as industrial
process control, air quality monitoring, environmental safety, and medical diagnostics.
Specifically, in industrial and environmental applications, the detection of harmful
gases is crucial for public health and safety. Thus, there is a significant demand for gas
sensors that are cost-effective, highly sensitive, and have rapid response times. These
sensors are vital in biomedical applications, particularly in diagnosing respiratory
diseases by detecting volatile organic bio-markers (VOCs) ranging from different
cancer types. Volatile Organic Compounds (VOCs) are a broad category of organic
chemicals that easily evaporate at room temperature due to their high vapor pressure.
These compounds are emitted by a variety of sources, both natural and man-made,
including paints, cleaning supplies, pesticides, building materials, and furnishings.
VOCs are also produced by burning fuel such as gasoline, wood, coal, or natural gas.
The evaporation of these compounds contributes to air pollution and can form
secondary pollutants such as ground-level ozone. Exposure to high levels of VOCs can
lead to health issues such as eye, nose, and throat irritation, headaches, and more severe
impacts like damage to the liver, kidney, and central nervous system. Some VOCs,
like benzene and formaldehyde, are also recognized as carcinogens, making their
control and regulation critical for indoor and outdoor air quality management.
In this study, platforms that can be used in many application areas have been produced
using thin-film deposition methods on a single silicon wafer; methods such as
multilayer photolithography, PVD (e-beam), PECVD, electrochemical methods,
successive integration, ICP-RIE dry etching, and metallization were utilized. A gas
sensor application was selected to check whether the produced platform was working.
The first stage of microfabrication is the implementation of cleaning procedures
suitable for the substrate to be used. In this thesis work, cleaning of the silicon substrate
involved the use of acetone, deionized water, isopropyl alcohol (IPA), nitrogen, and oxygen plasma. Cleaning stages for the 4-inch silicon wafer were completed, and then
initially for the construction of the micro heater, a double spiral square pattern was
drawn on a special platform and saved in the GDSII file format to the photolithography
device. Subsequently, 2 µm SiO2 / 30 nm Ti / 30 nm Au metals were coated using the
e-beam method. Titanium and gold metals were chosen to ensure adherence to the
surface in the construction of platinum micro heaters. One of the most significant
challenges encountered in the production of platinum thin films is undoubtedly the
cracking that occurs in the film structure as the thickness increases. Addressing this
problem forms the fundamental motivation of this thesis work. As an alternative to
traditional production techniques, we anticipate that platinum can be used as a heating
element by coating it using the electroplating technique. Aspects such as the continuity
of the film structure, whether it achieves the desired current density, and life testing
will be examined within our thesis work. For the purpose of demonstrating the use of
the heater structures produced in the sensor field, SnO2 and PANI materials will be
used. The use of SnO2 and PANI is not intended to develop sensor materials but solely
for performance demonstration.
In recent years, the global market for gas sensors has been continuously growing due
to the increasing demand in the application areas we have detailed. This growth is
robustly supported by factors such as the global emergence of air pollution as a health
problem, the enhancement of safety standards in workplaces, the development of
awareness regarding indoor air quality, industrialization and urbanization, and the
increasing demand for gas sensors in the chemical, energy, and environmental
monitoring industries.After the PVD processes, the micro heater pattern was created
on the structure via non-invert printing using the photolithography method. Si3N4
material was selected as the passivation material and was established as the base of the
IDE platform using the PECVD method. For the IDE pattern, an IDT interlocking
parallel electrode pattern was selected, and structures were created after the PVD
coatings and photolithography process. The synthesis, doping, and coating of the
relevant materials on the sensor platform were successfully performed using
hydrothermal and dripping methods. The electroactive polymer Polyaniline, found in
its emeraldine base form, was processed with HCl to transition from an insulating to a
conductive form and doped with SnO2 and ZnO metal oxides to prepare the coating on
the sensor platform.
As a result of the study, platinum micro heaters capable of reaching a maximum
temperature of 417℃ in one minute were produced on a 300 µm Si-wafer with
dimensions of 2.2 mm width and 4.8 mm length, layered with 2 µm SiO2 / 30 nm Ti /
30 nm Au / 600 nm Pt. Life testing for micro heaters was conducted, and for the first
three days, the structure was observed to not short circuit when subjected to a voltage
of 5V. After three days, the voltage was increased to 7V, and observations continued
for another one month and fifteen days. No short circuit condition was observed in the
operation system of the micro heater. Temperature characterizations of the platinum
micro heaters were conducted using both our own circuit and a thermal camera. From
the measurement results, the α constant for platinum metal was calculated as 0.00345
℃-1. Due to the stacking technology, 250 nm thick Si3N4 passivation material was
used, and the produced micro heaters were annealed at 200℃ and 400℃ for 2 hours.
Multilayered (100 nm Ti / 100 nm Au) IDEs were produced and integrated onto the
Si3N4 intermediate layer. For this platform, initially, cuts of 2 mm width and 2 mm
length were made from a 300 µm thick Si-wafer to prevent heat loss from the micro
heater systems, and then they were stacked on top of each other, after which wire bonder bonding techniques were performed with 25 µm Au wires. Electroactive
polymers and metal oxides were used for the gas sensor application. The synthesis
parts of PANI, SnO2 materials were performed (for PANI, the emeraldine base
insulating form was processed with HCl to become conductive) and PANI, PANI /
SnO2, PANI / ZnO metal oxide nano-composite gas sensors were produced with
different ratios of 1:1 mg and 1:5 mg using commercially available ZnO material.
These gas sensors were tested against gases important for industrial process control,
air quality monitoring, environmental safety like NO2, and gases important for
respiratory diseases such as acetone, ethanol, humidity, and chloroform. Current-time
response graphs were analyzed using MATLAB code. Measurements were taken at
room temperature and at 55℃ for pure gases and for these gases exposed to 30%, 50%,
70% humidity concentrations, and bar graphs were obtained. According to the
literature research results for the newly created system, it can be used as a platform for
many application areas and as a sub-platform for diagnosing diseases requiring
important diagnosis such as lung cancer, diabetes, and COPD. The primary goal of the
thesis was achieved by successfully implementing the MEMS micro heater integrated
IDE system platform. The secondary goal of the thesis includes the results of the gas
sensor application to understand whether this platform works. For the gas sensor
application, first, the synthesis of materials was performed, and coatings were made
using the dripping method. Synthesis and characterization of commercial PANI,
PANI-HCl, SnO2, PANI/SnO2, PANI/ZnO structures were carried out and three types
of sensor production were completed. These sensors were tested against acetone,
ethanol, chloroform, and NO2 gases to determine their selectivity. The sensitivities of
all sensors to gases are excellent. Bar graphs are included in the results and discussion
section. According to the graphic results, our PANI/SnO2 nano-composite sensor
behaved selectively even under conditions of 70% humidity at 55℃ for gases like
acetone, ethanol, and chloroform. The thesis work will make a significant contribution
by increasing the accessibility of this technology, thus improving public safety and
environmental sustainability. Developing low-cost and high-performance gas sensors
enhances the feasibility of gas detection systems and promotes their widespread use,
paving a promising path for the future of sensing technologies.