Semiconductor Device Using Oxide Semiconductor Memory
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Solution Overview
Problem
Current semiconductor memory devices face limitations in retaining data without power, high power consumption due to frequent refresh operations, and limitations in the number of writing operations in non-volatile memory devices, particularly in flash memory and MRAM.
Innovation Solution
A semiconductor device utilizing an oxide semiconductor material for memory circuits to reduce off-state current, combined with a peripheral circuit using a different semiconductor material for high-speed operation, eliminating the need for refresh operations and high voltage writing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If flash memory is used for non-volatile storage, then data holding period is extremely long and refresh operation is not needed, but the gate insulating layer deteriorates by tunneling current after a predetermined number of writing operations
Solution Approach 1:
The patent changes the fundamental writing mechanism from tunneling current injection (flash memory) to field-effect transistor switching (oxide semiconductor memory). This parameter change in the writing principle eliminates tunneling current damage to the gate insulating layer while maintaining non-volatile data storage capability through extremely low off-state current.
2Duration of action of stationary object
If flash memory is used for non-volatile storage, then high voltage is necessary to inject or remove charge, but this requires a circuit for generating high voltage and slows down writing and erasing operations
Solution Approach 1:
The patent extracts and eliminates the high voltage generation circuit from the memory system by using oxide semiconductor transistors that can achieve non-volatile storage with standard voltage levels. The field-effect switching mechanism requires only low voltage to control the channel current, removing the need for complex high voltage generation circuits.
3Duration of action of stationary object
If MRAM is used for non-volatile storage, then data can be retained without power, but it consumes a comparatively large amount of current in writing operation
Solution Approach 1:
The patent changes the writing mechanism from magnetic field switching (MRAM) to electric field-controlled current switching (oxide semiconductor memory). This parameter change reduces writing current consumption by using the high on/off current ratio of oxide semiconductor transistors to control charge storage and retrieval without requiring large currents for magnetic switching.
4Ease of manufacture
If DRAM is used for volatile storage, then writing operation is simple, but leakage current flows between source and drain when transistor is in off state, making data holding period short and requiring frequent refresh operations
Solution Approach 1:
The patent uses composite material structure combining oxide semiconductor layer with conventional semiconductor materials to create a transistor with extremely low off-state current. The oxide semiconductor channel layer provides high on-state current for simple writing operations while maintaining extremely low off-state current for long data holding period without refresh operations.
5Duration of action of stationary object
If SRAM is used for volatile storage, then refresh operation is not needed, but cost per storage capacity is increased due to complex circuit such as flip-flop
Solution Approach 1:
The patent changes the storage mechanism from active flip-flop circuit (SRAM) to passive charge storage with field-effect control (oxide semiconductor memory). This parameter change eliminates the need for complex flip-flop circuits while achieving non-volatile storage through extremely low leakage current, reducing both circuit complexity and cell size.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enables long-term data retention, reduced power consumption, and high-speed operation without the limitations of conventional memory devices, such as flash memory and MRAM, by using oxide semiconductor material in memory circuits and other semiconductor materials for peripheral circuits.
Implementation Method 1
a memory circuit is formed using a material which allows a sufficient reduction in the off-state current of a transistor, e.g., an oxide semiconductor material which is a wide bandgap semiconductor
Implementation Method 2
A flash memory includes a floating gate between a gate electrode and a channel formation region in a transistor and stores data by holding electric charge in the floating gate
Implementation Method 3
a gate insulating layer included in a storage element deteriorates by tunneling current generated in writing
Data Source
AI summary
Provided is a semiconductor device with a novel structure in which stored data can be retained even when power is not supplied, and which does not have a limitation on the number of writing. The semiconductor device includes both a memory circuit including a transistor including an oxide semiconductor (in a broader sense, a transistor whose off-state current is sufficiently small), and a peripheral circuit such as a driver circuit including a transistor including a material other than an oxide semiconductor (that is, a transistor capable of operating at sufficiently high speed). Further, the peripheral circuit is provided in a lower portion and the memory circuit is provided in an upper portion, so that the area and size of the semiconductor device can be decreased.