Embedded Flash for IoT Application

IoT (Internet of Thing) Introduction

The Internet of Thing (IoT), at times referred to as Internet of Everything (IoE), can be considered as a highly intelligent application beyond that of Machine-to-Machine (M2M) communication, and which covers a variety of protocols, domains, and applications. Basically, IoT covers with MCU (ALU+ RAM+ embedded Flash), connectivity and sensor (MEMS) as illustrated in chart 1. As some research reports’ prediction, a great quantity of IoT will be used in the coming future in M2M, payment system, transportation, product manufacture, inventory management, machinery monitoring, shipment, livestock, energy saving, for smart city, smart building, smart energy, smart industry, smart finance and smart health. Recently published research articles estimated that there will be 50 billion devices connected to the internet as IoT by 2020.

IoT devices need to sense information, connect to the internet, analyze factors, manage element and store data, therefore many IC and components will be demanded to fulfill specific requirements and stringent specifications. Basically, low power consumption, small footprint and cost effectiveness are “MUST” factors in IoT devices. Thus, all components in IoT devices should move in the direction of low power, small footprint and low cost.

Highly Integerated SOC for IoT Application

In general, IoT system contains MCU, RF, Flash senor IC and other components. However commercial Flash requires Vdd=1.8V or 3.3V, and it causes MCU operate with high Vdd (>1.8V). IoTMemory's eFlash solution only requires Vdd=1.2V or 0.9V, which can help to integerate MCU, RF and Flash as SOC to reduce IC size and then take out some passive components on the system, as chart 2.

The Benefits of IoTMemory NOR Flash Solution: SilvoFlash^TM

․ Reduce Power Consumption:
The highly efficient embedded Flash (SilvoFlash^TM) allows to reduce MCU Vdd and hence lower power consumption effectively.

․ Reduce System Footprint:
Instead of using two 1.5V batteries to operate MCU, SilvoFlash^TM can enable MCU to operate with a single battery, and then reduce overall system area.

․ Reduce Cost:
In general, other commercial Flash technologies require an extra 11~12 mask layers to implement an embedded flash scheme. SilvoFlash^TM only takes requirements an additional 5~6 mask layers, depending on process platform. A highly integrated MCU also helps to reduce cost in IC bonding, testing, capacitance, inductance and etc.

Thus, the requiremets of eFlash in IoT must fulfill low power consumption, small footprint and low cost, as chart 3.

SilvoFlash^TM Technology

SilvoFlash^TM means “Single low voltages Flash”, which is formed using 3D split gate Nor Flash, a tunneling oxidation layer, a floating gate, an inter-gate dielectric layer, and a control gate that are sequentially deposited on a substrate, as chart 4. Each flash cell of SilvoFlash^TM is operated with 5 terminals, common source (CS), drain (BL), control gate (CG), word line (WL) and erase poly (EP). Both flash cells are shared with the same CG and CS to reduce bitcell size. When performing a programming or erasing operation to the flash memory device, appropriate voltages are applied to a source region, a drain region, and the control gate, such that electrons are injected into the polysilicon floating gate or pulled out from the polysilicon floating gate.

SilvoFlash^TM cell requires a single low Vdd input at 1.2V (LP) or 0.9V (ULP). It only requires 1.2V Vdd in Read, no need any boost or charge-pumping circuit.  SilvoFlash^TM uses source side injection for programming and FN for erasing; the mechanisms of PG and ER help SilvoFlash^TM have high endurance ( >100K cycling) and high data retention ( >10 years with -40C~85C, next step with -40C~125C).

SilvoFlash^TM Macro Design

To meet embedded Flash requirements in IoT application, SilvoFlash^TM macro design has been designed with consideration for low power, low voltages supply, small footprint, low cost, fast start-up time and secure data storage. Macro block of SilvoFlash^TM is as seen in chart 5.

․ Read Mode:

To differentiate the flash cell in “ON” or “OFF” state in Read mode, the reference Vt of cell is set as 0, as chart 6. With SilvoFlash^TM cell, the bias condition is only required Vdd in Read, without any boost or charge-pump circuit needed.

․ Programming and Erasing Mode:

High Gate Coupling Ratio (GCR) of SilvoFlash^TM helps to make programming and erasing more efficient, resulting in reduced operation voltages. To create operation voltages of SilvoFlash^TM to be under 7V, positive and negative bias voltages are used in the circuit, which also helps to save power and energy significantly.

SilvoFlash^TM - Ideally Flash Memory for IoT Application

Author Biography

Alan Cheng (Cheng Yu-Ming), James Cheng (Cheng Tzung-Wen) and Adam Huang (Huang I-Hsin) from IoTMemory Technology Inc., July 2015.