RF Characteristic Analysis Model Extraction on the Stacked Metal–Insulator–Metal Capacitors for Radio Frequency Applications

This brief aimed to report study results of radio frequency integrated circuit applicability through RF characteristic analysis model extraction on the stacked metal-insulator- metal (MIM) capacitor. We used analysis method enhancing capacitance density per unit area via a parallel connection of two MIM capacitors vertically. The total capacitance of the stacked MIM capacitor was 2.05 fF/μm² and leakage current and breakdown voltage were 0.004 fA/μm² and more than 50 V, respectively. Moreover, VCC1 showed a value less than 40 ppm/V, while VCC2 showed a value less than 20 ppm/V². Temperature coefficient of capacitance exhibited values less than 80 ppm/°C for every 25 °C increase between 25 °C and 125 °C. A specialized equivalent circuit with the parallel connection of MIM capacitance (CMIM1, CMIM2) was proposed for the stacked MIM capacitor. When extracted model parameter components were simulated, high accuracy was exhibited despite increased frequency by applying various parasitic components to the extraction.

I. Introduction

The conventional single-band single-mode modulation pattern of radio frequency (RF) devices are rapidly changing to the multiband multimode modulation pattern along with the rapid advancement of wireless communication [1], [2]. Hence, many studies are continuously being conducted since the RF devices need to fulfill various indispensable requisites, such as high performance, miniaturization, light-weight, low power and cost, and so on. The RF units used in the Si-based radio frequency integrated circuit (RFIC) are mainly classified into active elements and passive elements [3], [4]. One of the leading silicon-based active elements is the complementary metal–oxide–semiconductor field effect transistor (CMOSFET) and main passive elements are the resistor, inductor, capacitor, and others. Among those, the capacitor used for various purposes in RFIC is a very crucial passive element utilized in the impedance matching circuit and the dc block of the bias circuit. In addition, it effected on the bypass circuit for low frequency oscillation prevention and noise feature enhancement, and the degeneration circuit for stability and linearity increases. The metal–insulator–metal (MIM) capacitor enables precise capacitance and desirable voltage coefficient of capacitance (VCC), temperature coefficient of capacitance (TCC), and leakage current. However, the MIM capacitor takes too much space along with inductors and two solutions have been studied to overcome the disadvantages. One of the ways is changing the type or thickness of the insulator to enhance capacitance density [5], [6]. The other way is applying diverse structural designing methods of the MIM capacitor to improve capacitance density per unit area [7]–[9]. This brief examined the stacked MIM capacitor, one of the structural designing methods of the MIM capacitor that enhances capacitance density per unit area via a parallel connection of two MIM capacitors vertically. Moreover, this brief aimed to assess the performance through characteristization of the stacked MIM capacitor. Also, we evaluate the applicability to RFIC through model extraction using an equivalent circuit suggested by RF characteristic analysis of the stacked MIM capacitor. In addition, this brief extracted an improved model of the stacked MIM capacitor by proposing a specialized equivalent circuit representing stacked MIM capacitors.