COMMON STOCK SUBSCRIPTION AGREEMENT

EXHIBIT 4.15

AMERIGON INCORPORATED

COMMON STOCK SUBSCRIPTION AGREEMENT

THIS COMMON STOCK SUBSCRIPTION AGREEMENT (this “Agreement”) is entered into as of June 27, 2003, by and among Amerigon Incorporated, a California corporation (the “Company”), and Ferrotec Corporation, a Japanese corporation (the “Purchaser”).

RECITALS

WHEREAS, the Company has authorized the sale and issuance of an aggregate of 1,000,000 shares of its Common Stock (the “Shares”) in a private placement pursuant to Regulation S under the Securities Act of 1933;

WHEREAS, Purchaser desires to purchase, and the Company desires to issue and sell, the Shares on the terms and conditions set forth herein; and

NOW, THEREFORE, in consideration of the foregoing recitals and the mutual promises hereinafter set forth, the parties hereto agree as follows:

SECTION 1. PURCHASE AND SALE OF STOCK.

1.1 Authorization of Shares. The Company has authorized the sale and issuance to Purchaser of the Shares.

1.2 Sale and Purchase. Subject to the terms and conditions hereof, the Company hereby agrees to issue and sell to Purchaser, and Purchaser agrees to purchase from the Company, the Shares. In exchange for the Shares, Purchaser shall pay to the Company an aggregate purchase price of US $2,500,000 (the “Purchase Price”) or US $2.50 per Share.

SECTION 2. CLOSING.

2.1 Closing. The closing of the sale and purchase of the Shares under this Agreement (the “Closing”) will take place at the offices of the Purchaser on June 27, 2003 (such date is hereinafter referred to as the “Closing Date”).

2.2 Delivery. At the Closing, subject to the terms and conditions hereof, the Company will deliver to Purchaser certificates representing the number of Shares to be purchased at the Closing by Purchaser, against payment of the Purchase Price by check or wire transfer made payable to the order of the Company, or any combination of the foregoing.

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SECTION 3. REPRESENTATIONS, WARRANTIES AND COVENANTS OF THE COMPANY.

The Company hereby represents, warrants and covenants to Purchaser as follows:

3.1 Organization, Good Standing, Corporate Power, Qualification and Subsidiaries. The Company is a corporation duly organized, validly existing and in good standing under the laws of the State of California. The Company has all requisite corporate power and authority to own and operate its properties and assets, to execute and deliver this Agreement, to issue and sell the Shares and to carry out the provisions of this Agreement and to carry out its business as presently conducted and as presently proposed to be conducted. The Company is duly qualified and is authorized to do business and is in good standing as a foreign corporation in all jurisdictions in which the nature of its activities and of its properties (both owned and leased) makes such qualification necessary, except for those jurisdictions in which failure to do so would not have a material adverse effect on the Company or its business.

3.2 Due Authorization and Issuance. The Shares have been duly authorized for issuance and sale to Purchaser pursuant to this Agreement, and, when issued and delivered by the Company against payment therefor in accordance with the terms of this Agreement, will be duly and validly issued and fully paid and nonassessable, and will be sold free and clear of any pledge, lien, security interest, encumbrance, claim or equitable interest. No further approval or authorization of any shareholder or the Board of Directors of the Company is required for the issuance and sale or transfer of the Shares.

3.3 Authorization; Binding Obligations. All corporate action on the part of the Company, its officers, directors and shareholders necessary for the authorization, sale and issuance of the Shares pursuant hereto and for the performance of the Company’s obligations hereunder has been taken or will be taken prior to the Closing. This Agreement, when executed and delivered, will be valid and binding obligations of the Company enforceable in accordance with their terms, except (i) as limited by applicable bankruptcy, insolvency, reorganization, moratorium or other laws of general application affecting enforcement of creditors’ rights; (ii) general principles of equity that restrict the availability of equitable remedies; and (iii) to the extent that enforceability may be limited by applicable laws.

3.4 Offering Valid. Assuming the accuracy of the representations and warranties of Purchaser contained in Section 4 hereof, the offer, sale and issuance of the Shares will be exempt from the registration requirements of the Securities Act of 1933, as amended (the “Securities Act”), and will have been registered or qualified (or are exempt from registration and qualification) under the registration, permit or qualification requirements of all applicable state securities laws. The Company will not engage in any directed selling efforts (as defined in Regulation S under the Securities Act) with respect to the Shares. The Company has complied and will comply with the offering restrictions requirement of Regulation S (Rule 901 through Rule 905 and Preliminary Notes) of the Securities Act (“Regulation S”).

SECTION 4. REPRESENTATIONS, WARRANTIES AND COVENANTS OF PURCHASER.

Purchaser hereby represents, warrants and covenants to the Company as follows:

4.1 Requisite Power and Authority. Purchaser has all necessary power and authority under all applicable provisions of law to execute and deliver this Agreement and to carry out its provisions. All actions on Purchaser’s part required for the lawful execution and

delivery of this Agreement have been or will be effectively taken prior to the Closing. Upon their execution and delivery, this Agreement will be valid and binding obligations of Purchaser, enforceable in accordance with their terms, except (i) as limited by applicable bankruptcy, insolvency, reorganization, moratorium or other laws of general application affecting enforcement of creditors’ rights, (ii) general principles of equity that restrict the availability of equitable remedies, and (iii) to the extent that enforceability may be limited by applicable laws.

4.2 Investment Representations. Purchaser understands that the Shares have not been registered under the Securities Act. Purchaser also understands that the Shares are being offered and sold pursuant to an exemption from registration contained in the Securities Act based in part upon Purchaser’s representations contained in the Agreement. Purchaser represents that (a) the offer to sell the Shares to Purchaser was not made to a person in the United States, (b) Purchaser was outside the United States at the time its agreement to purchase was originated, and (c) no directed selling efforts (as defined in Regulation S) directed at Purchaser were made in the United States by the Company, any of its affiliates or any person acting on behalf of the Company.

4.3 Accredited Investor. Purchaser represents that it is an accredited investor within the meaning of Regulation D under the Securities Act.

4.4 Purchaser Bears Economic Risk. Purchaser has substantial experience in evaluating and investing in private placement transactions of securities in companies similar to the Company so that it is capable of evaluating the merits and risks of its investment in the Company and has the capacity to protect its own interests. Purchaser must bear the economic risk of this investment indefinitely unless the Shares are registered pursuant to the Securities Act, or exemption from registration is available.

4.5 Acquisition for Own Account. Purchaser is not a U.S. person, as defined in Rule 902(k) of Regulation S of the Securities Act, and is acquiring the Shares for Purchaser’s own account for investment only and not for the account or benefit of any U.S. Person or with a view towards their distribution.

4.6 Receipt of Company Information. Purchaser has had an opportunity to discuss the Company’s business, management and financial affairs with directors, officers and management of the Company and has had the opportunity to review the Company’s operations and facilities. Purchaser has also had the opportunity to ask questions of and receive answers from the Company and its management regarding the terms and conditions of this investment. Purchaser has reviewed the Form 10-K, Annual Report to Security Holders and Proxy Statement for the period ended December 31, 2002 and Form 10-Q for the period ended March 31, 2003, filed by the Company with the Securities and Exchange Commission (SEC) and any 8-K filings made by the Company with the SEC since the date of filing of such Form 10-K. The foregoing, however, does not limit or modify the representations and warranties of the Company in Section 3 of this Agreement or the right of Purchaser to rely thereon.

4.7 No Public Market. Purchaser acknowledges and agrees that the Shares must be held indefinitely unless they are subsequently registered under the Securities Act or an exemption from such registration is available. Purchaser understands that the Company has no

present intention of registering the Shares, or any shares of its Common Stock. Purchaser also understands that there is no assurance that any exemption from registration under the Securities Act will be available and that, even if available, such exemption may not allow Purchaser to transfer all or any portion of the Shares under the circumstances, in the amounts or at the times Purchaser might propose. Purchaser has been advised or is aware of the provisions of Rule 144 promulgated under the Securities Act, which permits limited resale of shares purchased in a private placement subject to the satisfaction of certain conditions, including, among other things: the availability of certain current public information about the Company, the resale occurring not less than one year after a party has purchased and paid for the security to be sold, the sale being through an unsolicited “broker’s transaction” or in transactions directly with a market maker (as said term is defined under the Securities Exchange Act of 1934, as amended) and the number of shares being sold during any three-month period not exceeding specified limitations.

4.8 Transfer Restrictions. Purchaser acknowledges and agrees that the Shares are subject to restrictions on transfer as set forth in this Section 4.8 and in Appendix A hereto. Purchaser understands that: (a) the Shares shall not be offered, sold or transferable in the absence compliance with the provisions of Regulation S, pursuant to registration under the Securities Act, or pursuant to an exemption therefrom or in the absence of compliance with any term of this Agreement; (b) the Company shall provide stop transfer instructions to its transfer agent (the “Transfer Agent”) with respect to the Shares in order to enforce the restrictions contained in this Section 4.8 and in Appendix A hereto; (c) hedging transactions involving the Shares may not be conducted unless in compliance with the Securities Act; and (d) each certificate representing Shares shall be in the name of Purchaser and shall bear substantially the following legends (in addition to any legends required under applicable securities laws):

“THE SECURITIES REPRESENTED BY THIS CERTIFICATE HAVE NOT BEEN REGISTERED UNDER THE UNITED STATES OF AMERICA SECURITIES ACT OF 1933, AS AMENDED (THE “SECURITIES ACT”). THE SECURITIES REPRESENTED BY THIS CERTIFICATE SHALL NOT BE OFFERED OR SOLD IN THE UNITED STATES (AS DEFINED UNDER SECTIONS 230.901 THROUGH 230.904 OF TITLE 17 OF THE UNITED STATES CODE OF FEDERAL REGULATIONS (“REGULATION S”) OR OFFERED, SOLD, DELIVERED, PLEDGED OR OTHERWISE TRANSFERRED EXCEPT PURSUANT TO REGULATION S, PURSUANT TO REGISTRATION UNDER THE SECURITIES ACT OR PURSUANT TO AN EXEMPTION FROM THE REGISTRATION REQUIREMENTS OF THE SECURITIES ACT. HEDGING TRANSACTION INVOLVING THE SECURITIES REPRESENTED BY THIS CERTIFICATE MAY NOT BE CONDUCTED UNLESS IN COMPLIANCE WITH THE SECURITIES ACT. THIS CERTIFICATE MAY NOT BE OFFERED, SOLD, DELIVERED, PLEDGED OR OTHERWISE TRANSFERRED TO OR HELD BY ANY ENTITY, THE ASSETS OF WHICH ARE DEEMED TO INCLUDE THE ASSETS OF ANY EMPLOYEE BENEFIT PLAN THAT IS SUBJECT TO THE U.S. EMPLOYEE RETIREMENT INCOME SECURITY ACT OF 1974 (“ERISA”). EACH HOLDER OF THIS CERTIFICATE WHO IS A U.S. PERSON IS HEREBY NOTIFIED THAT, EXCEPT AS PROVIDED IN THE AGREEMENT, SUCH HOLDER SHALL NOT BE ENTITLED TO RECEIVE

ANY PAYMENTS UNDER THIS CERTIFICATE. BY ITS ACCEPTANCE OF THIS CERTIFICATE, EACH HOLDER OF THIS CERTIFICATES SHALL BE DEEMED TO HAVE REPRESENTED TO AMERIGON INCORPORATED THAT SUCH HOLDER EITHER IS NOT A U.S. PERSON AND THAT SUCH HOLDER IS NOT PURCHASING THIS CERTIFICATE FOR THE ACCOUNT OF ANY U.S. PERSON OR IS ACQUIRING THIS SECURITY IN A TRANSACTION THAT IS EXEMPT FROM THE REGISTRATION REQUIREMENTS OF THE SECURITIES ACT.

ANY UNITED STATES PERSON WHO HOLDS THIS OBLIGATION WILL BE SUBJECT TO LIMITATIONS UNDER THE UNITED STATES INCOME TAX LAWS, INCLUDING THE LIMITATIONS PROVIDED IN SECTIONS 165(j) AND 1287(a) OF THE INTERNAL REVENUE CODE.”

SECTION 5. REGISTRATION RIGHTS.

5.1 Demand Registration.

(a) Subject to the provisions set forth in this Section 5.1, if the Company shall receive a written request from Purchaser that the Company effect the registration under the Securities Act on Form S-3 of all of the Purchaser’s Shares and specifying the intended method of disposition thereof (a “Demand Registration”), then the Company shall use its reasonable best efforts to effect, as expeditiously as possible, the registration under the Securities Act on Form S-3 of the Registrable Shares with the Securities and Exchange Commission (the “SEC”) which the Company has been so requested to register by Purchaser then held by Purchaser, all to the extent necessary to permit the disposition (in accordance with the intended methods thereof as aforesaid) of the Registrable Shares so to be registered.

Purchaser may, at any time prior to the effective date of the registration statement relating to such registration, revoke a request for such registration, without liability, by providing a written notice to the Company revoking such request, in which case such request, so revoked, shall be considered a Demand Registration unless such revocation arose out of the fault of the Company or unless Purchaser reimburses the Company for all costs incurred by the Company in connection with such registration, in which case such request shall not be considered a Demand Registration.

(b) The Company will not be required to effect more than one Demand Registration, and Purchaser shall not be entitled to request a Demand Registration until one year after the Closing. The Company will not be obligated to effect a Demand Registration (1) if the Registrable Securities requested by Purchaser to be registered have an anticipated aggregate offering price to the public (before deducting any underwriter discounts, concessions or commissions) of less than $1,000,000 or (2) if Form S-3 is not available for such offering.

(c) Upon written notice to Purchaser, the Company may, as a matter of right, postpone effecting a registration pursuant to this Section 5.1 on one occasion during any period of six consecutive months for a reasonable time specified in the notice but not exceeding 90 days (which period may not be extended or renewed except th