## 1 Introduction  
Respiration, the process of gas exchange between an organism and the environment, is critical for sustaining human life and activity [1]. Shortness of breath is a form of discomfort caused by breathing difficulties. Respiratory disorders exhibit various symptoms depending on their cause. Asthma, heart conditions such as heart failure, pneumonia, bronchitis, sleep apnea, fever due to infection, and various other diseases and health conditions can cause respiratory disorders [2]. When experiencing shortness of breath, a feeling of air depletion accompanies an increase in the breathing rate, making alterations in the depth of breathing possible. Breathing causes changes in humidity depending on inhalation and exhalation. Therefore, humidity detection is becoming an increasingly important method of respiratory monitoring, as it offers a promising approach to establish a relationship between human breathing and electrical signals [3]. In addition to work, health and safety, and the analysis of human emotions, respiratory monitoring has also found applications in sports performance and training. The monitoring of breathing during exercise can provide valuable information on the efficiency of breathing patterns and the intensity of exercise. This can help athletes and coaches to optimize training programs and improve performance. For example, tracking respiratory rates during high-intensity interval training can help athletes to determine their optimal rest periods between exercise to maximize the effectiveness of the workout. Furthermore, respiratory monitoring has been used in the diagnosis and management of various medical conditions and problems. For example, in sleep therapy, respiratory monitoring is used to diagnose and treat sleep apnea, a condition in which a person's breathing repeatedly stops and starts during sleep. In cardiology, respiratory monitoring can provide information on heart function and help to diagnose heart conditions. In addition, respiratory monitoring can also be used to monitor the effects of medications on respiratory function and to assess the progression of respiratory diseases, such as chronic obstructive pulmonary disease and asthma. However, to measure 20-30 breaths per minute, a fast response time is required. Nonetheless, the existing humidity sensors have limitations, such as their large size, low sensitivity, sensitivity to temperature changes, and slow response times, which limit their application fields [4]. Through the studies on microelectromechanical systems (MEMS) over the past few decades, miniature humidity sensors have been developed using several different principles, such as capacitance, resistance, resonance, piezoelectric, and optical sensors [1; 2; 5; 6; 7; 8]. Methods for measuring the moisture generated from direct respiration are divided into two types, depending on the measurement technology used: capacitive and resistive electronic humidity sensors. Capacitive humidity sensors are widely used because of advantages related to their temperature stability, low power consumption, excellent linearity, and wide range of relative humidity measurements [9]. However, their structure is complex, and the management of the capacitance values is challenging, making the manufacturing process complicated and resulting in high numbers of errors due to small changes, which remains an issue to be resolved [10]. Resistive humidity sensors enable precise measurements and are easy to manufacture at low costs. They are also small in size with high degrees of freedom and are suitable for sensor arrays. Owing to these advantages, research is being conducted to replace capacitive humidity sensors with resistive humidity sensors [11; 12; 13]. Indeed, many issues remain to be addressed in regard to the resistance-type humidity sensors that have been studied for metal oxides and polymers. These issues include a low response rate, low reactivity in low-humidity environments, hysteresis, and susceptibility to external environmental factors.