B0150810

Page 1

Invention Journal of Research Technology in Engineering & Management (IJRTEM) ISSN: 2455-3689 www.ijrtem.com Volume 1 Issue 5 Ç July. 2016 Ç PP 08-10

SCR-Based ESD Protection Designs for RF ICs Chun-Yu Lin Department of Electrical Engineering, National Taiwan Normal University, Taipei, Taiwan

Abstract: CMOS technology has been used to implement the radio-frequency integrated circuits (RF ICs). However, it was known that advanced CMOS technologies seriously degrade the electrostatic discharge (ESD) robustness of ICs. Therefore, on-chip ESD protection devices must be added into the chip, including RF ICs. To minimize the impacts from ESD protection devices on RF performances, the ESD protection at RF pads must be carefully designed. A review on ESD protection designs with silicon-controlled rectifier (SCR) devices in RF ICs is presented in this article. Keywords: CMOS, ESD, RF, SCR. I. Introduction All integrated circuits (ICs), including radio-frequency (RF) ICs, must meet the reliability specifications during mass production. Electrostatic discharge (ESD), which is one of the most important reliability issues during mass production, must be taken into consideration [1]. All integrated circuits used in the wireless communication products need to be equipped with ESD protection designs. However, ESD protections cause RF performance degradation with several undesired effects. Parasitic capacitance is one of the most important design considerations for RF ICs. A typical specification for a giga-Hertz RF circuit on human-body-model (HBM) ESD robustness and the maximum parasitic capacitance of ESD protection device are 2kV and 200fF, respectively [2], [3]. As the operating frequencies of RF circuits increase, the parasitic capacitance is more strictly limited. The ESD protection devices used in commercial CMOS processes include the diode, MOS, BJT, field-oxide device, and silicon-controlled rectifier (SCR). Among the ESD protection devices, the SCR device has been reported to be useful for RF ESD protection design due to its higher ESD robustness within a smaller layout area and lower parasitic capacitance [4]. In this paper, the SCR-based ESD protection designs for 30GHz and 60GHz applications are reviewed.

II. SCR Device The device structure of the SCR device used in RF input (RFIN) pad is illustrated in Fig. 1(a). The SCR path between RFIN and VSS consists of P+, N-well, P-well, and N+. The equivalent circuit of the SCR consists of a PNP BJT (QPNP) and a NPN BJT (QNPN), as shown in Fig. 1(b). As ESD zapping from RFIN to VSS, the positive-feedback regenerative mechanism of QPNP and QNPN results in the SCR device highly conductive to make SCR very robust against ESD stresses. However, SCR has some drawbacks, such as higher trigger voltage and slower turn-on speed. To reduce the trigger voltage of an SCR device, the trigger signal can be sent into the base terminal of QNPN to enhance the turn-on speed [5].

(a)

(b)

Fig. 1. (a) Device cross-sectional view, and (b) equivalent circuit, of SCR device used in RF input pad.

III. SCR-Based ESD Protection Design for 30GHz Applications An inductor-assisted SCR (LASCR) has been presented for 30GHz applications. Fig. 2 shows the design of LASCR, which consists of an SCR, an inductor (L), and a diode string (Dtrig) [6]. The diode string is used to enhance the turn-on efficiency of SCR [7]. As ESD zapping from RFIN to VSS, the inductor and diode string will discharge the initial ESD current, and then the SCR will be triggered on to discharge the primary ESD current. Under normal RF operating condition, the inductor will resonate with the parasitic capacitance of

| Volume 1| Issue 5 |

www.ijrtem.com

| July 2016| 8


Turn static files into dynamic content formats.

Create a flipbook
Issuu converts static files into: digital portfolios, online yearbooks, online catalogs, digital photo albums and more. Sign up and create your flipbook.